Run E2E tests for server execution as well as WebAssembly. Fixes several

server-execution bugs uncovered by the E2E tests.

src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Boot.Server.ts

@@ -17,7 +17,7 @@ function boot() {
   });
 
   connection = new signalR.HubConnectionBuilder()
-    .withUrl('/_blazor')
+    .withUrl('_blazor')
     .withHubProtocol(new MessagePackHubProtocol())
     .configureLogging(signalR.LogLevel.Information)
     .build();

src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Rendering/RenderBatch/OutOfProcessRenderBatch.ts

@@ -118,7 +118,8 @@ class OutOfProcessRenderTreeFrameReader implements RenderTreeFrameReader {
   }
 
   elementReferenceCaptureId(frame: RenderTreeFrame) {
-    return readInt32LE(this.batchDataUint8, frame as any + 4); // 2nd int
+    const stringIndex = readInt32LE(this.batchDataUint8, frame as any + 4); // 2nd int
+    return this.stringReader.readString(stringIndex);
   }
 
   componentId(frame: RenderTreeFrame) {
@@ -159,14 +160,15 @@ class OutOfProcessStringReader {
   }
 
   readString(index: number): string | null {
-    const stringTableEntry = readInt32LE(this.batchDataUint8, this.stringTableStartIndex + index * stringTableEntryLength);
+    if (index === -1) { // Special value encodes 'null'
-    if (stringTableEntry === -1) { // Special value encodes 'null'
       return null;
     } else {
+      const stringTableEntryPos = readInt32LE(this.batchDataUint8, this.stringTableStartIndex + index * stringTableEntryLength);
+
       // By default, .NET's BinaryWriter gives LEB128-length-prefixed UTF-8 data.
       // This is convenient enough to decode in JavaScript.
-      const numUtf8Bytes = readLEB128(this.batchDataUint8, stringTableEntry);
+      const numUtf8Bytes = readLEB128(this.batchDataUint8, stringTableEntryPos);
-      const charsStart = stringTableEntry + numLEB128Bytes(numUtf8Bytes);
+      const charsStart = stringTableEntryPos + numLEB128Bytes(numUtf8Bytes);
       const utf8Data = new DataView(
         this.batchDataUint8.buffer,
         this.batchDataUint8.byteOffset + charsStart,

src/Microsoft.AspNetCore.Blazor.Server/Circuits/RenderBatchWriter.cs

@@ -138,7 +138,21 @@ namespace Microsoft.AspNetCore.Blazor.Server.Circuits
             {
                 case RenderTreeFrameType.Attribute:
                     WriteString(frame.AttributeName);
-                    WriteString(frame.AttributeValue as string);
+                    if (frame.AttributeValue is bool boolValue)
+                    {
+                        // Encoding the bool as either "" or null is pretty odd, but avoids
+                        // having to pack any "what type of thing is this" info into the same
+                        // 4 bytes as the string table index. If, later, we need a way of
+                        // distinguishing whether an attribute value is really a bool or a string
+                        // or something else, we'll need a different encoding mechanism. Since there
+                        // would never be more than (say) 2^28 (268 million) distinct string table
+                        // entries, we could use the first 4 bits to encode the value type.
+                        WriteString(boolValue ? string.Empty : null);
+                    }
+                    else
+                    {
+                        WriteString(frame.AttributeValue as string);
+                    }
                     _binaryWriter.Write(frame.AttributeEventHandlerId);
                     break;
                 case RenderTreeFrameType.Component:

src/Microsoft.JSInterop/DotNetDispatcher.cs

@@ -72,14 +72,25 @@ namespace Microsoft.JSInterop
                 ? null
                 : jsRuntimeBaseInstance.ArgSerializerStrategy.FindDotNetObject(dotNetObjectId);
 
-            var syncResult = InvokeSynchronously(assemblyName, methodIdentifier, targetInstance, argsJson);
+            object syncResult = null;
+            Exception syncException = null;
+
+            try
+            {
+                syncResult = InvokeSynchronously(assemblyName, methodIdentifier, targetInstance, argsJson);
+            }
+            catch (Exception ex)
+            {
+                syncException = ex;
+            }
 
             // If there was no callId, the caller does not want to be notified about the result
             if (callId != null)
             {
                 // Invoke and coerce the result to a Task so the caller can use the same async API
                 // for both synchronous and asynchronous methods
-                var task = syncResult is Task syncResultTask ? syncResultTask : Task.FromResult(syncResult);
+                var task = CoerceToTask(syncResult, syncException);
+
                 task.ContinueWith(completedTask =>
                 {
                     try
@@ -96,6 +107,22 @@ namespace Microsoft.JSInterop
             }
         }
 
+        private static Task CoerceToTask(object syncResult, Exception syncException)
+        {
+            if (syncException != null)
+            {
+                return Task.FromException(syncException);
+            }
+            else if (syncResult is Task syncResultTask)
+            {
+                return syncResultTask;
+            }
+            else
+            {
+                return Task.FromResult(syncResult);
+            }
+        }
+
         private static object InvokeSynchronously(string assemblyName, string methodIdentifier, object targetInstance, string argsJson)
         {
             if (targetInstance != null)

test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/BasicTestAppTestBase.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using BasicTestApp;
@@ -11,13 +11,14 @@ using Xunit.Abstractions;
 
 namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure
 {
-    public class BasicTestAppTestBase : ServerTestBase<DevHostServerFixture<Program>>
+    public class BasicTestAppTestBase : ServerTestBase<ToggleExecutionModeServerFixture<Program>>
     {
-        public const string ServerPathBase = "/subdir";
+        public string ServerPathBase
+            => "/subdir" + (_serverFixture.UsingAspNetHost ? "#server" : "");
 
         public BasicTestAppTestBase(
             BrowserFixture browserFixture,
-            DevHostServerFixture<Program> serverFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
@@ -27,19 +28,18 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure
         protected IWebElement MountTestComponent<TComponent>() where TComponent : IComponent
         {
             var componentTypeName = typeof(TComponent).FullName;
-            WaitUntilDotNetRunningInBrowser();
+            var testSelector = WaitUntilTestSelectorReady();
-            ((IJavaScriptExecutor)Browser).ExecuteScript(
+            testSelector.SelectByValue("none");
-                $"mountTestComponent('{componentTypeName}')");
+            testSelector.SelectByValue(componentTypeName);
             return Browser.FindElement(By.TagName("app"));
         }
 
-        protected void WaitUntilDotNetRunningInBrowser()
+        protected SelectElement WaitUntilTestSelectorReady()
         {
-            new WebDriverWait(Browser, TimeSpan.FromSeconds(30)).Until(driver =>
+            var elemToFind = By.CssSelector("#test-selector > select");
-            {
+            new WebDriverWait(Browser, TimeSpan.FromSeconds(30)).Until(
-                return ((IJavaScriptExecutor)driver)
+                driver => driver.FindElement(elemToFind) != null);
-                    .ExecuteScript("return window.isTestReady;");
+            return new SelectElement(Browser.FindElement(elemToFind));
-            });
         }
     }
 }

test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/BrowserFixture.cs

@@ -39,6 +39,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure
             try
             {
                 var driver = new RemoteWebDriver(opts);
+                driver.Manage().Timeouts().ImplicitWait = TimeSpan.FromSeconds(1);
                 Browser = driver;
                 Logs = new RemoteLogs(driver);
             }

test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/ServerFixtures/ToggleExecutionModeServerFixture.cs

@@ -0,0 +1,49 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures
+{
+    public class ToggleExecutionModeServerFixture<TClientProgram>
+        : ServerFixture
+    {
+        public string PathBase { get; set; }
+        public bool UsingAspNetHost { get; private set; }
+
+        private AspNetSiteServerFixture.BuildWebHost _buildWebHostMethod;
+        private IDisposable _serverToDispose;
+
+        public void UseAspNetHost(AspNetSiteServerFixture.BuildWebHost buildWebHostMethod)
+        {
+            _buildWebHostMethod = buildWebHostMethod
+                ?? throw new ArgumentNullException(nameof(buildWebHostMethod));
+            UsingAspNetHost = true;
+        }
+
+        protected override string StartAndGetRootUri()
+        {
+            if (_buildWebHostMethod == null)
+            {
+                // Use Blazor's dev host server
+                var underlying = new DevHostServerFixture<TClientProgram>();
+                underlying.PathBase = PathBase;
+                _serverToDispose = underlying;
+                return underlying.RootUri.AbsoluteUri;
+            }
+            else
+            {
+                // Use specified ASP.NET host server
+                var underlying = new AspNetSiteServerFixture();
+                underlying.BuildWebHostMethod = _buildWebHostMethod;
+                _serverToDispose = underlying;
+                return underlying.RootUri.AbsoluteUri;
+            }
+        }
+
+        public override void Dispose()
+        {
+            _serverToDispose.Dispose();
+        }
+    }
+}

test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/ServerTestBase.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures;
@@ -12,7 +12,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure
         : BrowserTestBase, IClassFixture<TServerFixture>
         where TServerFixture: ServerFixture
     {
-        private readonly TServerFixture _serverFixture;
+        protected readonly TServerFixture _serverFixture;
 
         public ServerTestBase(BrowserFixture browserFixture, TServerFixture serverFixture, ITestOutputHelper output)
             : base(browserFixture, output)
@@ -33,6 +33,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure
                 }
             }
 
+            Browser.Navigate().GoToUrl("about:blank");
             Browser.Navigate().GoToUrl(absoluteUrl);
         }
     }

test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/WaitAssert.cs

@@ -0,0 +1,70 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using OpenQA.Selenium;
+using OpenQA.Selenium.Support.UI;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure
+{
+    // XUnit assertions, but hooked into Selenium's polling mechanism
+
+    public class WaitAssert
+    {
+        private readonly static TimeSpan DefaultTimeout = TimeSpan.FromSeconds(1);
+
+        public static void Equal<T>(T expected, Func<T> actual)
+            => WaitAssertCore(() => Assert.Equal(expected, actual()));
+
+        public static void True(Func<bool> actual)
+            => WaitAssertCore(() => Assert.True(actual()));
+
+        public static void False(Func<bool> actual)
+            => WaitAssertCore(() => Assert.False(actual()));
+
+        public static void Contains(string expectedSubstring, Func<string> actualString)
+            => WaitAssertCore(() => Assert.Contains(expectedSubstring, actualString()));
+
+        public static void Collection<T>(Func<IEnumerable<T>> actualValues, params Action<T>[] elementInspectors)
+            => WaitAssertCore(() => Assert.Collection(actualValues(), elementInspectors));
+
+        public static void Empty(Func<IEnumerable> actualValues)
+            => WaitAssertCore(() => Assert.Empty(actualValues()));
+
+        public static void Single(Func<IEnumerable> actualValues)
+            => WaitAssertCore(() => Assert.Single(actualValues()));
+
+        private static void WaitAssertCore(Action assertion, TimeSpan timeout = default)
+        {
+            if (timeout == default)
+            {
+                timeout = DefaultTimeout;
+            }
+
+            try
+            {
+                new WebDriverWait(BrowserTestBase.Browser, timeout).Until(_ =>
+                {
+                    try
+                    {
+                        assertion();
+                        return true;
+                    }
+                    catch
+                    {
+                        return false;
+                    }
+                });
+            }
+            catch (WebDriverTimeoutException)
+            {
+                // Instead of reporting it as a timeout, report the Xunit exception
+                assertion();
+            }
+        }
+    }
+}

test/Microsoft.AspNetCore.Blazor.E2ETest/ServerExecutionTests/ServerExecutionTestExtensions.cs

@@ -0,0 +1,16 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures;
+
+namespace Microsoft.AspNetCore.Blazor.E2ETest.ServerExecutionTests
+{
+    internal static class ServerExecutionTestExtensions
+    {
+        public static ToggleExecutionModeServerFixture<T> WithServerExecution<T>(this ToggleExecutionModeServerFixture<T> serverFixture)
+        {
+            serverFixture.UseAspNetHost(TestServer.Program.BuildWebHost);
+            return serverFixture;
+        }
+    }
+}

test/Microsoft.AspNetCore.Blazor.E2ETest/ServerExecutionTests/ServerSideAppTest.cs

@@ -10,23 +10,20 @@ using System.Linq;
 using Xunit;
 using Xunit.Abstractions;
 
-namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
+namespace Microsoft.AspNetCore.Blazor.E2ETest.ServerExecutionTests
 {
-    public class ServerSideBlazorTest : ServerTestBase<AspNetSiteServerFixture>, IDisposable
+    public class ServerSideAppTest : ServerTestBase<AspNetSiteServerFixture>
     {
-        private readonly AspNetSiteServerFixture _serverFixture;
+        public ServerSideAppTest(
-
-        public ServerSideBlazorTest(
             BrowserFixture browserFixture,
             AspNetSiteServerFixture serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
-            _serverFixture = serverFixture;
             _serverFixture.Environment = AspNetEnvironment.Development;
             _serverFixture.BuildWebHostMethod = ServerSideBlazor.Server.Program.BuildWebHost;
 
-            Navigate("/", noReload: true);
+            Navigate("/", noReload: false);
             WaitUntilLoaded();
         }
 
@@ -58,13 +55,13 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Browser.FindElement(By.LinkText("Counter")).Click();
 
             // Verify we're now on the counter page, with that nav link (only) highlighted
-            Assert.Equal("Counter", Browser.FindElement(mainHeaderSelector).Text);
+            WaitAssert.Equal("Counter", () => Browser.FindElement(mainHeaderSelector).Text);
             Assert.Collection(Browser.FindElements(activeNavLinksSelector),
                 item => Assert.Equal("Counter", item.Text));
 
             // Verify we can navigate back to home too
             Browser.FindElement(By.LinkText("Home")).Click();
-            Assert.Equal("Hello, world!", Browser.FindElement(mainHeaderSelector).Text);
+            WaitAssert.Equal("Hello, world!", () => Browser.FindElement(mainHeaderSelector).Text);
             Assert.Collection(Browser.FindElements(activeNavLinksSelector),
                 item => Assert.Equal("Home", item.Text));
         }
@@ -74,7 +71,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         {
             // Navigate to "Counter"
             Browser.FindElement(By.LinkText("Counter")).Click();
-            Assert.Equal("Counter", Browser.FindElement(By.TagName("h1")).Text);
+            WaitAssert.Equal("Counter", () => Browser.FindElement(By.TagName("h1")).Text);
 
             // Observe the initial value is zero
             var countDisplayElement = Browser.FindElement(By.CssSelector("h1 + p"));
@@ -83,17 +80,19 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Click the button; see it counts
             var button = Browser.FindElement(By.CssSelector(".main button"));
             button.Click();
+            WaitAssert.Equal("Current count: 1", () => countDisplayElement.Text);
             button.Click();
+            WaitAssert.Equal("Current count: 2", () => countDisplayElement.Text);
             button.Click();
-            Assert.Equal("Current count: 3", countDisplayElement.Text);
+            WaitAssert.Equal("Current count: 3", () => countDisplayElement.Text);
         }
 
-        [Fact(Skip = "This is failing and I don't know why")]
+        [Fact]
         public void HasFetchDataPage()
         {
             // Navigate to "Fetch Data"
             Browser.FindElement(By.LinkText("Fetch data")).Click();
-            Assert.Equal("Weather forecast", Browser.FindElement(By.TagName("h1")).Text);
+            WaitAssert.Equal("Weather forecast", () => Browser.FindElement(By.TagName("h1")).Text);
 
             // Wait until loaded
             var tableSelector = By.CssSelector("table.table");
@@ -115,12 +114,5 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             new WebDriverWait(Browser, TimeSpan.FromSeconds(30)).Until(
                 driver => driver.FindElement(By.TagName("app")).Text != "Loading...");
         }
-
-        public void Dispose()
-        {
-            // Make the tests run faster by navigating back to the home page when we are done
-            // If we don't, then the next test will reload the whole page before it starts
-            Browser.FindElement(By.LinkText("Home")).Click();
-        }
     }
 }

test/Microsoft.AspNetCore.Blazor.E2ETest/ServerExecutionTests/TestSubclasses.cs

@@ -0,0 +1,59 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using BasicTestApp;
+using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures;
+using Microsoft.AspNetCore.Blazor.E2ETest.Tests;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Blazor.E2ETest.ServerExecutionTests
+{
+    public class ServerComponentRenderingTest : ComponentRenderingTest
+    {
+        public ServerComponentRenderingTest(BrowserFixture browserFixture, ToggleExecutionModeServerFixture<Program> serverFixture, ITestOutputHelper output)
+            : base(browserFixture, serverFixture.WithServerExecution(), output)
+        {
+        }
+    }
+
+    public class ServerBindTest : BindTest
+    {
+        public ServerBindTest(BrowserFixture browserFixture, ToggleExecutionModeServerFixture<Program> serverFixture, ITestOutputHelper output)
+            : base(browserFixture, serverFixture.WithServerExecution(), output)
+        {
+        }
+    }
+
+    public class ServerEventBubblingTest : EventBubblingTest
+    {
+        public ServerEventBubblingTest(BrowserFixture browserFixture, ToggleExecutionModeServerFixture<Program> serverFixture, ITestOutputHelper output)
+            : base(browserFixture, serverFixture.WithServerExecution(), output)
+        {
+        }
+    }
+
+    public class ServerEventTest : EventTest
+    {
+        public ServerEventTest(BrowserFixture browserFixture, ToggleExecutionModeServerFixture<Program> serverFixture, ITestOutputHelper output)
+            : base(browserFixture, serverFixture.WithServerExecution(), output)
+        {
+        }
+    }
+
+    public class ServerInteropTest : InteropTest
+    {
+        public ServerInteropTest(BrowserFixture browserFixture, ToggleExecutionModeServerFixture<Program> serverFixture, ITestOutputHelper output)
+            : base(browserFixture, serverFixture.WithServerExecution(), output)
+        {
+        }
+    }
+
+    public class ServerRoutingTest : RoutingTest
+    {
+        public ServerRoutingTest(BrowserFixture browserFixture, ToggleExecutionModeServerFixture<Program> serverFixture, ITestOutputHelper output)
+            : base(browserFixture, serverFixture.WithServerExecution(), output)
+        {
+        }
+    }
+}

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/BinaryHttpClientTest.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using BasicTestApp.HttpClientTest;
@@ -22,7 +22,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
         public BinaryHttpClientTest(
             BrowserFixture browserFixture,
-            DevHostServerFixture<BasicTestApp.Program> devHostServerFixture,
+            ToggleExecutionModeServerFixture<BasicTestApp.Program> devHostServerFixture,
             AspNetSiteServerFixture apiServerFixture,
             ITestOutputHelper output)
             : base(browserFixture, devHostServerFixture, output)

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/BindTest.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using BasicTestApp;
@@ -14,12 +14,13 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
     public class BindTest : BasicTestAppTestBase
     {
         public BindTest(
-            BrowserFixture browserFixture, 
+            BrowserFixture browserFixture,
-            DevHostServerFixture<Program> serverFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
-            Navigate(ServerPathBase, noReload: true);
+            // On WebAssembly, page reloads are expensive so skip if possible
+            Navigate(ServerPathBase, noReload: !serverFixture.UsingAspNetHost);
             MountTestComponent<BindCasesComponent>();
         }
         
@@ -39,12 +40,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Assert.Equal(string.Empty, boundValue.Text); // Doesn't update until change event
             Assert.Equal(string.Empty, mirrorValue.GetAttribute("value"));
             target.SendKeys("\t");
-            Assert.Equal("Changed value", boundValue.Text);
+            WaitAssert.Equal("Changed value", () => boundValue.Text);
             Assert.Equal("Changed value", mirrorValue.GetAttribute("value"));
 
             // Remove the value altogether
             setNullButton.Click();
-            Assert.Equal(string.Empty, target.GetAttribute("value"));
+            WaitAssert.Equal(string.Empty, () => target.GetAttribute("value"));
             Assert.Equal(string.Empty, boundValue.Text);
             Assert.Equal(string.Empty, mirrorValue.GetAttribute("value"));
         }
@@ -63,12 +64,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Modify target; verify value is updated and that textboxes linked to the same data are updated
             target.Clear();
             target.SendKeys("Changed value\t");
-            Assert.Equal("Changed value", boundValue.Text);
+            WaitAssert.Equal("Changed value", () => boundValue.Text);
             Assert.Equal("Changed value", mirrorValue.GetAttribute("value"));
 
             // Remove the value altogether
             setNullButton.Click();
-            Assert.Equal(string.Empty, target.GetAttribute("value"));
+            WaitAssert.Equal(string.Empty, () => target.GetAttribute("value"));
             Assert.Equal(string.Empty, boundValue.Text);
             Assert.Equal(string.Empty, mirrorValue.GetAttribute("value"));
         }
@@ -85,7 +86,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             target.SendKeys("Changed value");
             Assert.Equal(string.Empty, boundValue.Text); // Don't update as there's no change event fired yet.
             target.SendKeys("\t");
-            Assert.Equal("Changed value", boundValue.Text);
+            WaitAssert.Equal("Changed value", () => boundValue.Text);
         }
 
         [Fact]
@@ -99,7 +100,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Modify target; verify value is updated
             target.Clear();
             target.SendKeys("Changed value\t");
-            Assert.Equal("Changed value", boundValue.Text);
+            WaitAssert.Equal("Changed value", () => boundValue.Text);
         }
 
         [Fact]
@@ -113,12 +114,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Modify target; verify value is updated
             target.Click();
-            Assert.True(target.Selected);
+            WaitAssert.True(() => target.Selected);
             Assert.Equal("True", boundValue.Text);
 
             // Modify data; verify checkbox is updated
             invertButton.Click();
-            Assert.False(target.Selected);
+            WaitAssert.False(() => target.Selected);
             Assert.Equal("False", boundValue.Text);
         }
 
@@ -133,12 +134,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Modify target; verify value is updated
             target.Click();
-            Assert.False(target.Selected);
+            WaitAssert.False(() => target.Selected);
             Assert.Equal("False", boundValue.Text);
 
             // Modify data; verify checkbox is updated
             invertButton.Click();
-            Assert.True(target.Selected);
+            WaitAssert.True(() => target.Selected);
             Assert.Equal("True", boundValue.Text);
         }
 
@@ -152,13 +153,13 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Modify target; verify value is updated
             target.SelectByText("Third choice");
-            Assert.Equal("Third", boundValue.Text);
+            WaitAssert.Equal("Third", () => boundValue.Text);
 
             // Also verify we can add and select new options atomically
             // Don't move this into a separate test, because then the previous assertions
             // would be dependent on test execution order (or would require a full page reload)
             Browser.FindElement(By.Id("select-box-add-option")).Click();
-            Assert.Equal("Fourth", boundValue.Text);
+            WaitAssert.Equal("Fourth", () => boundValue.Text);
             Assert.Equal("Fourth choice", target.SelectedOption.Text);
         }
 
@@ -175,7 +176,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Modify target; verify value is updated and that textboxes linked to the same data are updated
             target.Clear();
             target.SendKeys("42\t");
-            Assert.Equal("42", boundValue.Text);
+            WaitAssert.Equal("42", () => boundValue.Text);
             Assert.Equal("42", mirrorValue.GetAttribute("value"));
         }
 
@@ -192,7 +193,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Modify target; verify value is updated and that textboxes linked to the same data are updated
             target.Clear();
             target.SendKeys("-3000000000\t");
-            Assert.Equal("-3000000000", boundValue.Text);
+            WaitAssert.Equal("-3000000000", () => boundValue.Text);
             Assert.Equal("-3000000000", mirrorValue.GetAttribute("value"));
         }
 
@@ -209,7 +210,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Modify target; verify value is updated and that textboxes linked to the same data are updated
             target.Clear();
             target.SendKeys("-3.141\t");
-            Assert.Equal("-3.141", boundValue.Text);
+            WaitAssert.Equal("-3.141", () => boundValue.Text);
             Assert.Equal("-3.141", mirrorValue.GetAttribute("value"));
         }
 
@@ -226,14 +227,14 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Modify target; verify value is updated and that textboxes linked to the same data are updated
             target.Clear();
             target.SendKeys("-3.14159265359\t");
-            Assert.Equal("-3.14159265359", boundValue.Text);
+            WaitAssert.Equal("-3.14159265359", () => boundValue.Text);
             Assert.Equal("-3.14159265359", mirrorValue.GetAttribute("value"));
 
             // Modify target; verify value is updated and that textboxes linked to the same data are updated
             // Double shouldn't preserve trailing zeros
             target.Clear();
             target.SendKeys("0.010\t");
-            Assert.Equal("0.01", boundValue.Text);
+            WaitAssert.Equal("0.01", () => boundValue.Text);
             Assert.Equal("0.01", mirrorValue.GetAttribute("value"));
         }
 
@@ -251,7 +252,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Decimal should preserve trailing zeros
             target.Clear();
             target.SendKeys("0.010\t");
-            Assert.Equal("0.010", boundValue.Text);
+            WaitAssert.Equal("0.010", () => boundValue.Text);
             Assert.Equal("0.010", mirrorValue.GetAttribute("value"));
         }
     }

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/ComponentRenderingTest.cs

@@ -11,6 +11,7 @@ using BasicTestApp.HierarchicalImportsTest.Subdir;
 using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure;
 using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures;
 using OpenQA.Selenium;
+using OpenQA.Selenium.Support.UI;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -20,11 +21,11 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
     {
         public ComponentRenderingTest(
             BrowserFixture browserFixture,
-            DevHostServerFixture<Program> serverFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
-            Navigate(ServerPathBase, noReload: true);
+            Navigate(ServerPathBase, noReload: !serverFixture.UsingAspNetHost);
         }
 
         [Fact]
@@ -71,7 +72,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Clicking button increments count
             appElement.FindElement(By.TagName("button")).Click();
-            Assert.Equal("Current count: 1", countDisplayElement.Text);
+            WaitAssert.Equal("Current count: 1", () => countDisplayElement.Text);
         }
 
         [Fact]
@@ -84,11 +85,11 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Clicking 'tick' changes the state, and starts a task
             appElement.FindElement(By.Id("tick")).Click();
-            Assert.Equal("Started", stateElement.Text);
+            WaitAssert.Equal("Started", () => stateElement.Text);
 
             // Clicking 'tock' completes the task, which updates the state
             appElement.FindElement(By.Id("tock")).Click();
-            Assert.Equal("Stopped", stateElement.Text);
+            WaitAssert.Equal("Stopped", () => stateElement.Text);
         }
 
         [Fact]
@@ -103,12 +104,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Typing adds element
             inputElement.SendKeys("a");
-            Assert.Collection(liElements(),
+            WaitAssert.Collection(liElements,
                 li => Assert.Equal("a", li.Text));
 
             // Typing again adds another element
             inputElement.SendKeys("b");
-            Assert.Collection(liElements(),
+            WaitAssert.Collection(liElements,
                 li => Assert.Equal("a", li.Text),
                 li => Assert.Equal("b", li.Text));
 
@@ -127,17 +128,19 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Initial count is zero; clicking button increments count
             Assert.Equal("Current count: 0", countDisplayElement.Text);
             incrementButton.Click();
-            Assert.Equal("Current count: 1", countDisplayElement.Text);
+            WaitAssert.Equal("Current count: 1", () => countDisplayElement.Text);
 
             // We can remove an event handler
             toggleClickHandlerCheckbox.Click();
+            WaitAssert.Empty(() => appElement.FindElements(By.Id("listening-message")));
             incrementButton.Click();
-            Assert.Equal("Current count: 1", countDisplayElement.Text);
+            WaitAssert.Equal("Current count: 1", () => countDisplayElement.Text);
 
             // We can add an event handler
             toggleClickHandlerCheckbox.Click();
+            appElement.FindElement(By.Id("listening-message"));
             incrementButton.Click();
-            Assert.Equal("Current count: 2", countDisplayElement.Text);
+            WaitAssert.Equal("Current count: 2", () => countDisplayElement.Text);
         }
 
         [Fact]
@@ -164,7 +167,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Clicking increments count in child component
             appElement.FindElement(By.TagName("button")).Click();
-            Assert.Equal("Current count: 1", counterDisplay.Text);
+            WaitAssert.Equal("Current count: 1", () => counterDisplay.Text);
         }
 
         [Fact]
@@ -179,7 +182,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Clicking increments count in child element
             appElement.FindElement(By.TagName("button")).Click();
-            Assert.Equal("1", messageElementInChild.Text);
+            WaitAssert.Equal("1", () => messageElementInChild.Text);
         }
 
         [Fact]
@@ -192,12 +195,22 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Func<IEnumerable<IWebElement>> childComponentWrappers = () => appElement.FindElements(By.TagName("p"));
             Assert.Empty(childComponentWrappers());
 
-            // Click to add some child components
+            // Click to add/remove some child components
             addButton.Click();
+            WaitAssert.Collection(childComponentWrappers,
+                elem => Assert.Equal("Child 1", elem.FindElement(By.ClassName("message")).Text));
+
             addButton.Click();
+            WaitAssert.Collection(childComponentWrappers,
+                elem => Assert.Equal("Child 1", elem.FindElement(By.ClassName("message")).Text),
+                elem => Assert.Equal("Child 2", elem.FindElement(By.ClassName("message")).Text));
+
             removeButton.Click();
+            WaitAssert.Collection(childComponentWrappers,
+                elem => Assert.Equal("Child 1", elem.FindElement(By.ClassName("message")).Text));
+
             addButton.Click();
-            Assert.Collection(childComponentWrappers(),
+            WaitAssert.Collection(childComponentWrappers,
                 elem => Assert.Equal("Child 1", elem.FindElement(By.ClassName("message")).Text),
                 elem => Assert.Equal("Child 3", elem.FindElement(By.ClassName("message")).Text));
         }
@@ -215,7 +228,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // When property changes, child is renotified before rerender
             incrementButton.Click();
-            Assert.Equal("You supplied: 101", suppliedValueElement.Text);
+            WaitAssert.Equal("You supplied: 101", () => suppliedValueElement.Text);
             Assert.Equal("I computed: 202", computedValueElement.Text);
         }
 
@@ -225,8 +238,8 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Initially, the region isn't shown
             var appElement = MountTestComponent<RenderFragmentToggler>();
             var originalButton = appElement.FindElement(By.TagName("button"));
-            var fragmentElements = appElement.FindElements(By.CssSelector("p[name=fragment-element]"));
+            Func<IEnumerable<IWebElement>> fragmentElements = () => appElement.FindElements(By.CssSelector("p[name=fragment-element]"));
-            Assert.Empty(fragmentElements);
+            Assert.Empty(fragmentElements());
 
             // The JS-side DOM builder handles regions correctly, placing elements
             // after the region after the corresponding elements
@@ -234,13 +247,11 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // When we click the button, the region is shown
             originalButton.Click();
-            fragmentElements = appElement.FindElements(By.CssSelector("p[name=fragment-element]"));
+            WaitAssert.Single(fragmentElements);
-            Assert.Single(fragmentElements);
 
             // The button itself was preserved, so we can click it again and see the effect
             originalButton.Click();
-            fragmentElements = appElement.FindElements(By.CssSelector("p[name=fragment-element]"));
+            WaitAssert.Empty(fragmentElements);
-            Assert.Empty(fragmentElements);
         }
 
         [Fact]
@@ -263,11 +274,13 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // .NET code access to browser APIs
             var showPromptButton = appElement.FindElements(By.TagName("button")).First();
             showPromptButton.Click();
-            var modal = Browser.SwitchTo().Alert();
+            
+            var modal = new WebDriverWait(Browser, TimeSpan.FromSeconds(3))
+                .Until(SwitchToAlert);
             modal.SendKeys("Some value from test");
             modal.Accept();
             var promptResult = appElement.FindElement(By.TagName("strong"));
-            Assert.Equal("Some value from test", promptResult.Text);
+            WaitAssert.Equal("Some value from test", () => promptResult.Text);
 
             // NuGet packages can also embed entire Blazor components (themselves
             // authored as Razor files), including static content. The CSS value
@@ -280,7 +293,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             var externalComponentButton = specialStyleDiv.FindElement(By.TagName("button"));
             Assert.Equal("Click me", externalComponentButton.Text);
             externalComponentButton.Click();
-            Assert.Equal("It works", externalComponentButton.Text);
+            WaitAssert.Equal("It works", () => externalComponentButton.Text);
         }
 
         [Fact]
@@ -324,9 +337,9 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Assert.Equal(string.Empty, inputElement.GetAttribute("value"));
 
             buttonElement.Click();
-            Assert.Equal("Clicks: 1", inputElement.GetAttribute("value"));
+            WaitAssert.Equal("Clicks: 1", () => inputElement.GetAttribute("value"));
             buttonElement.Click();
-            Assert.Equal("Clicks: 2", inputElement.GetAttribute("value"));
+            WaitAssert.Equal("Clicks: 2", () => inputElement.GetAttribute("value"));
         }
 
         [Fact]
@@ -342,17 +355,16 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             // Remove the captured element
             checkbox.Click();
-            Assert.Empty(appElement.FindElements(By.Id("capturedElement")));
+            WaitAssert.Empty(() => appElement.FindElements(By.Id("capturedElement")));
 
             // Re-add it; observe it starts empty again
             checkbox.Click();
             var inputElement = appElement.FindElement(By.Id("capturedElement"));
-            Assert.NotNull(inputElement);
             Assert.Equal(string.Empty, inputElement.GetAttribute("value"));
 
             // See that the capture variable was automatically updated to reference the new instance
             buttonElement.Click();
-            Assert.Equal("Clicks: 1", inputElement.GetAttribute("value"));
+            WaitAssert.Equal("Clicks: 1", () => inputElement.GetAttribute("value"));
         }
 
         [Fact]
@@ -363,26 +375,27 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             var currentCountTextSelector = By.CssSelector("#child-component p:first-of-type");
             var resetButton = appElement.FindElement(By.Id("reset-child"));
             var toggleChildCheckbox = appElement.FindElement(By.Id("toggle-child"));
+            Func<string> currentCountText = () => appElement.FindElement(currentCountTextSelector).Text;
 
             // Verify the reference was captured initially
             appElement.FindElement(incrementButtonSelector).Click();
-            Assert.Equal("Current count: 1", appElement.FindElement(currentCountTextSelector).Text);
+            WaitAssert.Equal("Current count: 1", currentCountText);
             resetButton.Click();
-            Assert.Equal("Current count: 0", appElement.FindElement(currentCountTextSelector).Text);
+            WaitAssert.Equal("Current count: 0", currentCountText);
             appElement.FindElement(incrementButtonSelector).Click();
-            Assert.Equal("Current count: 1", appElement.FindElement(currentCountTextSelector).Text);
+            WaitAssert.Equal("Current count: 1", currentCountText);
 
             // Remove and re-add a new instance of the child, checking the text was reset
             toggleChildCheckbox.Click();
-            Assert.Empty(appElement.FindElements(incrementButtonSelector));
+            WaitAssert.Empty(() => appElement.FindElements(incrementButtonSelector));
             toggleChildCheckbox.Click();
-            Assert.Equal("Current count: 0", appElement.FindElement(currentCountTextSelector).Text);
+            WaitAssert.Equal("Current count: 0", currentCountText);
 
             // Verify we have a new working reference
             appElement.FindElement(incrementButtonSelector).Click();
-            Assert.Equal("Current count: 1", appElement.FindElement(currentCountTextSelector).Text);
+            WaitAssert.Equal("Current count: 1", currentCountText);
             resetButton.Click();
-            Assert.Equal("Current count: 0", appElement.FindElement(currentCountTextSelector).Text);
+            WaitAssert.Equal("Current count: 0", currentCountText);
         }
 
         [Fact]
@@ -392,5 +405,17 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             var inputElement = appElement.FindElement(By.TagName("input"));
             Assert.Equal("Value set after render", inputElement.GetAttribute("value"));
         }
+
+        static IAlert SwitchToAlert(IWebDriver driver)
+        {
+            try
+            {
+                return driver.SwitchTo().Alert();
+            }
+            catch (NoAlertPresentException)
+            {
+                return null;
+            }
+        }
     }
 }

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/EventBubblingTest.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using BasicTestApp;
@@ -20,12 +20,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         // the one that doesn't match the 'bubbles' flag on the received event object.
 
         public EventBubblingTest(
-            BrowserFixture browserFixture, 
+            BrowserFixture browserFixture,
-            DevHostServerFixture<Program> serverFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
-            Navigate(ServerPathBase, noReload: true);
+            Navigate(ServerPathBase, noReload: !serverFixture.UsingAspNetHost);
             MountTestComponent<EventBubblingComponent>();
         }
         
@@ -35,9 +35,9 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Browser.FindElement(By.Id("button-with-onclick")).Click();
 
             // Triggers event on target and ancestors with handler in upwards direction
-            Assert.Equal(
+            WaitAssert.Equal(
                 new[] { "target onclick", "parent onclick" },
-                GetLogLines());
+                GetLogLines);
         }
 
         [Fact]
@@ -46,9 +46,9 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Browser.FindElement(By.Id("button-without-onclick")).Click();
 
             // Triggers event on ancestors with handler in upwards direction
-            Assert.Equal(
+            WaitAssert.Equal(
                 new[] { "parent onclick" },
-                GetLogLines());
+                GetLogLines);
         }
 
         [Fact]
@@ -57,9 +57,9 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             TriggerCustomBubblingEvent("element-with-onsneeze", "sneeze");
 
             // Triggers event on target and ancestors with handler in upwards direction
-            Assert.Equal(
+            WaitAssert.Equal(
                 new[] { "target onsneeze", "parent onsneeze" },
-                GetLogLines());
+                GetLogLines);
         }
 
         [Fact]
@@ -68,9 +68,9 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             TriggerCustomBubblingEvent("element-without-onsneeze", "sneeze");
 
             // Triggers event on ancestors with handler in upwards direction
-            Assert.Equal(
+            WaitAssert.Equal(
                 new[] { "parent onsneeze" },
-                GetLogLines());
+                GetLogLines);
         }
 
         [Fact]
@@ -79,7 +79,9 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Browser.FindElement(By.Id("input-with-onfocus")).Click();
 
             // Triggers event only on target, not other ancestors with event handler
-            Assert.Equal(new[] { "target onfocus" }, GetLogLines());
+            WaitAssert.Equal(
+                new[] { "target onfocus" },
+                GetLogLines);
         }
 
         [Fact]
@@ -88,7 +90,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Browser.FindElement(By.Id("input-without-onfocus")).Click();
 
             // Triggers no event
-            Assert.Empty(GetLogLines());
+            WaitAssert.Empty(GetLogLines);
         }
 
         private string[] GetLogLines()

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/EventTest.cs

@@ -1,13 +1,11 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System;
 using BasicTestApp;
 using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure;
 using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures;
 using OpenQA.Selenium;
 using OpenQA.Selenium.Interactions;
-using OpenQA.Selenium.Support.UI;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -16,8 +14,8 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
     public class EventTest : BasicTestAppTestBase
     {
         public EventTest(
-            BrowserFixture browserFixture, 
+            BrowserFixture browserFixture,
-            DevHostServerFixture<Program> serverFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
@@ -38,13 +36,13 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // Focus the target, verify onfocusin is fired
             input.Click();
 
-            Assert.Equal("onfocus,onfocusin,", output.Text);
+            WaitAssert.Equal("onfocus,onfocusin,", () => output.Text);
 
             // Focus something else, verify onfocusout is also fired
             var other = Browser.FindElement(By.Id("other"));
             other.Click();
 
-            Assert.Equal("onfocus,onfocusin,onblur,onfocusout,", output.Text);
+            WaitAssert.Equal("onfocus,onfocusin,onblur,onfocusout,", () => output.Text);
         }
 
         [Fact]
@@ -65,7 +63,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
                 .MoveToElement(other);
 
             actions.Perform();
-            Assert.Equal("onmouseover,onmouseout,", output.Text);
+            WaitAssert.Equal("onmouseover,onmouseout,", () => output.Text);
         }
 
         [Fact]
@@ -84,7 +82,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
                 .MoveToElement(input, 10, 10);
 
             actions.Perform();
-            Assert.Contains("onmousemove,", output.Text);
+            WaitAssert.Contains("onmousemove,", () => output.Text);
         }
 
         [Fact]
@@ -103,12 +101,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             var actions = new Actions(Browser).ClickAndHold(input);
 
             actions.Perform();
-            Assert.Equal("onmousedown,", output.Text);
+            WaitAssert.Equal("onmousedown,", () => output.Text);
 
             actions = new Actions(Browser).Release(input);
 
             actions.Perform();
-            Assert.Equal("onmousedown,onmouseup,", output.Text);
+            WaitAssert.Equal("onmousedown,onmouseup,", () => output.Text);
         }
     }
 }

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/HttpClientTest.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using BasicTestApp.HttpClientTest;
@@ -24,7 +24,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
         public HttpClientTest(
             BrowserFixture browserFixture,
-            DevHostServerFixture<BasicTestApp.Program> devHostServerFixture,
+            ToggleExecutionModeServerFixture<BasicTestApp.Program> devHostServerFixture,
             AspNetSiteServerFixture apiServerFixture,
             ITestOutputHelper output)
             : base(browserFixture, devHostServerFixture, output)

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/InteropTest.cs

@@ -14,7 +14,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
     {
         public InteropTest(
             BrowserFixture browserFixture,
-            DevHostServerFixture<Program> serverFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
@@ -26,7 +26,42 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         public void CanInvokeDotNetMethods()
         {
             // Arrange
-            var expectedValues = new Dictionary<string, string>
+            var expectedAsyncValues = new Dictionary<string, string>
+            {
+                ["VoidParameterlessAsync"] = "[]",
+                ["VoidWithOneParameterAsync"] = @"[{""id"":1,""isValid"":false,""data"":{""source"":""Some random text with at least 1 characters"",""start"":1,""length"":1}}]",
+                ["VoidWithTwoParametersAsync"] = @"[{""id"":2,""isValid"":true,""data"":{""source"":""Some random text with at least 2 characters"",""start"":2,""length"":2}},2]",
+                ["VoidWithThreeParametersAsync"] = @"[{""id"":3,""isValid"":false,""data"":{""source"":""Some random text with at least 3 characters"",""start"":3,""length"":3}},3,123]",
+                ["VoidWithFourParametersAsync"] = @"[{""id"":4,""isValid"":true,""data"":{""source"":""Some random text with at least 4 characters"",""start"":4,""length"":4}},4,123,16]",
+                ["VoidWithFiveParametersAsync"] = @"[{""id"":5,""isValid"":false,""data"":{""source"":""Some random text with at least 5 characters"",""start"":5,""length"":5}},5,123,20,40]",
+                ["VoidWithSixParametersAsync"] = @"[{""id"":6,""isValid"":true,""data"":{""source"":""Some random text with at least 6 characters"",""start"":6,""length"":6}},6,123,24,48,6.25]",
+                ["VoidWithSevenParametersAsync"] = @"[{""id"":7,""isValid"":false,""data"":{""source"":""Some random text with at least 7 characters"",""start"":7,""length"":7}},7,123,28,56,7.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5]]",
+                ["VoidWithEightParametersAsync"] = @"[{""id"":8,""isValid"":true,""data"":{""source"":""Some random text with at least 8 characters"",""start"":8,""length"":8}},8,123,32,64,8.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5,7.5],{""source"":""Some random text with at least 7 characters"",""start"":9,""length"":9}]",
+                ["result1Async"] = @"[0.1,0.2]",
+                ["result2Async"] = @"[{""id"":1,""isValid"":false,""data"":{""source"":""Some random text with at least 1 characters"",""start"":1,""length"":1}}]",
+                ["result3Async"] = @"[{""id"":2,""isValid"":true,""data"":{""source"":""Some random text with at least 2 characters"",""start"":2,""length"":2}},2]",
+                ["result4Async"] = @"[{""id"":3,""isValid"":false,""data"":{""source"":""Some random text with at least 3 characters"",""start"":3,""length"":3}},3,123]",
+                ["result5Async"] = @"[{""id"":4,""isValid"":true,""data"":{""source"":""Some random text with at least 4 characters"",""start"":4,""length"":4}},4,123,16]",
+                ["result6Async"] = @"[{""id"":5,""isValid"":false,""data"":{""source"":""Some random text with at least 5 characters"",""start"":5,""length"":5}},5,123,20,40]",
+                ["result7Async"] = @"[{""id"":6,""isValid"":true,""data"":{""source"":""Some random text with at least 6 characters"",""start"":6,""length"":6}},6,123,24,48,6.25]",
+                ["result8Async"] = @"[{""id"":7,""isValid"":false,""data"":{""source"":""Some random text with at least 7 characters"",""start"":7,""length"":7}},7,123,28,56,7.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5]]",
+                ["result9Async"] = @"[{""id"":8,""isValid"":true,""data"":{""source"":""Some random text with at least 8 characters"",""start"":8,""length"":8}},8,123,32,64,8.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5,7.5],{""source"":""Some random text with at least 7 characters"",""start"":9,""length"":9}]",
+                ["AsyncThrowSyncException"] = @"""System.InvalidOperationException: Threw a sync exception!",
+                ["AsyncThrowAsyncException"] = @"""System.InvalidOperationException: Threw an async exception!",
+                ["SyncExceptionFromAsyncMethod"] = "Function threw a sync exception!",
+                ["AsyncExceptionFromAsyncMethod"] = "Function threw an async exception!",
+                ["resultReturnDotNetObjectByRefAsync"] = "1001",
+                ["instanceMethodThisTypeNameAsync"] = @"""JavaScriptInterop""",
+                ["instanceMethodStringValueUpperAsync"] = @"""MY STRING""",
+                ["instanceMethodIncomingByRefAsync"] = "123",
+                ["instanceMethodOutgoingByRefAsync"] = "1234",
+                ["stringValueUpperAsync"] = "MY STRING",
+                ["testDtoNonSerializedValueAsync"] = "99999",
+                ["testDtoAsync"] = "Same",
+                ["returnPrimitiveAsync"] = "123",
+            };
+
+            var expectedSyncValues = new Dictionary<string, string>
             {
                 ["VoidParameterless"] = "[]",
                 ["VoidWithOneParameter"] = @"[{""id"":1,""isValid"":false,""data"":{""source"":""Some random text with at least 1 characters"",""start"":1,""length"":1}}]",
@@ -37,15 +72,6 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
                 ["VoidWithSixParameters"] = @"[{""id"":6,""isValid"":true,""data"":{""source"":""Some random text with at least 6 characters"",""start"":6,""length"":6}},6,123,24,48,6.25]",
                 ["VoidWithSevenParameters"] = @"[{""id"":7,""isValid"":false,""data"":{""source"":""Some random text with at least 7 characters"",""start"":7,""length"":7}},7,123,28,56,7.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5]]",
                 ["VoidWithEightParameters"] = @"[{""id"":8,""isValid"":true,""data"":{""source"":""Some random text with at least 8 characters"",""start"":8,""length"":8}},8,123,32,64,8.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5,7.5],{""source"":""Some random text with at least 7 characters"",""start"":9,""length"":9}]",
-                ["VoidParameterlessAsync"] = "[]",
-                ["VoidWithOneParameterAsync"] = @"[{""id"":1,""isValid"":false,""data"":{""source"":""Some random text with at least 1 characters"",""start"":1,""length"":1}}]",
-                ["VoidWithTwoParametersAsync"] = @"[{""id"":2,""isValid"":true,""data"":{""source"":""Some random text with at least 2 characters"",""start"":2,""length"":2}},2]",
-                ["VoidWithThreeParametersAsync"] = @"[{""id"":3,""isValid"":false,""data"":{""source"":""Some random text with at least 3 characters"",""start"":3,""length"":3}},3,123]",
-                ["VoidWithFourParametersAsync"] = @"[{""id"":4,""isValid"":true,""data"":{""source"":""Some random text with at least 4 characters"",""start"":4,""length"":4}},4,123,16]",
-                ["VoidWithFiveParametersAsync"] = @"[{""id"":5,""isValid"":false,""data"":{""source"":""Some random text with at least 5 characters"",""start"":5,""length"":5}},5,123,20,40]",
-                ["VoidWithSixParametersAsync"] = @"[{""id"":6,""isValid"":true,""data"":{""source"":""Some random text with at least 6 characters"",""start"":6,""length"":6}},6,123,24,48,6.25]",
-                ["VoidWithSevenParametersAsync"] = @"[{""id"":7,""isValid"":false,""data"":{""source"":""Some random text with at least 7 characters"",""start"":7,""length"":7}},7,123,28,56,7.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5]]",
-                ["VoidWithEightParametersAsync"] = @"[{""id"":8,""isValid"":true,""data"":{""source"":""Some random text with at least 8 characters"",""start"":8,""length"":8}},8,123,32,64,8.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5,7.5],{""source"":""Some random text with at least 7 characters"",""start"":9,""length"":9}]",
                 ["result1"] = @"[0.1,0.2]",
                 ["result2"] = @"[{""id"":1,""isValid"":false,""data"":{""source"":""Some random text with at least 1 characters"",""start"":1,""length"":1}}]",
                 ["result3"] = @"[{""id"":2,""isValid"":true,""data"":{""source"":""Some random text with at least 2 characters"",""start"":2,""length"":2}},2]",
@@ -55,40 +81,29 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
                 ["result7"] = @"[{""id"":6,""isValid"":true,""data"":{""source"":""Some random text with at least 6 characters"",""start"":6,""length"":6}},6,123,24,48,6.25]",
                 ["result8"] = @"[{""id"":7,""isValid"":false,""data"":{""source"":""Some random text with at least 7 characters"",""start"":7,""length"":7}},7,123,28,56,7.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5]]",
                 ["result9"] = @"[{""id"":8,""isValid"":true,""data"":{""source"":""Some random text with at least 8 characters"",""start"":8,""length"":8}},8,123,32,64,8.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5,7.5],{""source"":""Some random text with at least 7 characters"",""start"":9,""length"":9}]",
-                ["result1Async"] = @"[0.1,0.2]",
-                ["result2Async"] = @"[{""id"":1,""isValid"":false,""data"":{""source"":""Some random text with at least 1 characters"",""start"":1,""length"":1}}]",
-                ["result3Async"] = @"[{""id"":2,""isValid"":true,""data"":{""source"":""Some random text with at least 2 characters"",""start"":2,""length"":2}},2]",
-                ["result4Async"] = @"[{""id"":3,""isValid"":false,""data"":{""source"":""Some random text with at least 3 characters"",""start"":3,""length"":3}},3,123]",
-                ["result5Async"] = @"[{""id"":4,""isValid"":true,""data"":{""source"":""Some random text with at least 4 characters"",""start"":4,""length"":4}},4,123,16]",
-                ["result6Async"] = @"[{""id"":5,""isValid"":false,""data"":{""source"":""Some random text with at least 5 characters"",""start"":5,""length"":5}},5,123,20,40]",
-                ["result7Async"] = @"[{""id"":6,""isValid"":true,""data"":{""source"":""Some random text with at least 6 characters"",""start"":6,""length"":6}},6,123,24,48,6.25]",
-                ["result8Async"] = @"[{""id"":7,""isValid"":false,""data"":{""source"":""Some random text with at least 7 characters"",""start"":7,""length"":7}},7,123,28,56,7.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5]]",
-                ["result9Async"] = @"[{""id"":8,""isValid"":true,""data"":{""source"":""Some random text with at least 8 characters"",""start"":8,""length"":8}},8,123,32,64,8.25,[0.5,1.5,2.5,3.5,4.5,5.5,6.5,7.5],{""source"":""Some random text with at least 7 characters"",""start"":9,""length"":9}]",
                 ["ThrowException"] = @"""System.InvalidOperationException: Threw an exception!",
-                ["AsyncThrowSyncException"] = @"""System.InvalidOperationException: Threw a sync exception!",
-                ["AsyncThrowAsyncException"] = @"""System.InvalidOperationException: Threw an async exception!",
                 ["ExceptionFromSyncMethod"] = "Function threw an exception!",
-                ["SyncExceptionFromAsyncMethod"] = "Function threw a sync exception!",
-                ["AsyncExceptionFromAsyncMethod"] = "Function threw an async exception!",
                 ["resultReturnDotNetObjectByRefSync"] = "1000",
-                ["resultReturnDotNetObjectByRefAsync"] = "1001",
                 ["instanceMethodThisTypeName"] = @"""JavaScriptInterop""",
                 ["instanceMethodStringValueUpper"] = @"""MY STRING""",
                 ["instanceMethodIncomingByRef"] = "123",
                 ["instanceMethodOutgoingByRef"] = "1234",
-                ["instanceMethodThisTypeNameAsync"] = @"""JavaScriptInterop""",
-                ["instanceMethodStringValueUpperAsync"] = @"""MY STRING""",
-                ["instanceMethodIncomingByRefAsync"] = "123",
-                ["instanceMethodOutgoingByRefAsync"] = "1234",
                 ["stringValueUpperSync"] = "MY STRING",
                 ["testDtoNonSerializedValueSync"] = "99999",
                 ["testDtoSync"] = "Same",
-                ["stringValueUpperAsync"] = "MY STRING",
-                ["testDtoNonSerializedValueAsync"] = "99999",
-                ["testDtoAsync"] = "Same",
                 ["returnPrimitive"] = "123",
-                ["returnPrimitiveAsync"] = "123",
             };
+
+            // Include the sync assertions only when running under WebAssembly
+            var expectedValues = expectedAsyncValues;
+            if (!_serverFixture.UsingAspNetHost)
+            {
+                foreach (var kvp in expectedSyncValues)
+                {
+                    expectedValues.Add(kvp.Key, kvp.Value);
+                }
+            }
+            
             var actualValues = new Dictionary<string, string>();
 
             // Act

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/RoutingTest.cs

@@ -15,25 +15,22 @@ using Xunit.Abstractions;
 
 namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 {
-    public class RoutingTest : BasicTestAppTestBase, IDisposable
+    public class RoutingTest : BasicTestAppTestBase
     {
-        private readonly ServerFixture _server;
-
         public RoutingTest(
-            BrowserFixture browserFixture, 
+            BrowserFixture browserFixture,
-            DevHostServerFixture<Program> serverFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
-            _server = serverFixture;
+            Navigate(ServerPathBase, noReload: false);
-            Navigate(ServerPathBase, noReload: true);
+            WaitUntilTestSelectorReady();
-            WaitUntilDotNetRunningInBrowser();
         }
 
         [Fact]
         public void CanArriveAtDefaultPage()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");
+            SetUrlViaPushState("/");
 
             var app = MountTestComponent<TestRouter>();
             Assert.Equal("This is the default page.", app.FindElement(By.Id("test-info")).Text);
@@ -47,7 +44,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             // servers to enforce a canonical URL (with trailing slash) for the homepage.
             // But in case they don't want to, we need to handle it the same as if the URL does
             // have a trailing slash.
-            SetUrlViaPushState($"{ServerPathBase}");
+            SetUrlViaPushState("");
 
             var app = MountTestComponent<TestRouter>();
             Assert.Equal("This is the default page.", app.FindElement(By.Id("test-info")).Text);
@@ -57,7 +54,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         [Fact]
         public void CanArriveAtPageWithParameters()
         {
-            SetUrlViaPushState($"{ServerPathBase}/WithParameters/Name/Ghi/LastName/O'Jkl");
+            SetUrlViaPushState("/WithParameters/Name/Ghi/LastName/O'Jkl");
 
             var app = MountTestComponent<TestRouter>();
             Assert.Equal("Your full name is Ghi O'Jkl.", app.FindElement(By.Id("test-info")).Text);
@@ -67,7 +64,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         [Fact]
         public void CanArriveAtNonDefaultPage()
         {
-            SetUrlViaPushState($"{ServerPathBase}/Other");
+            SetUrlViaPushState("/Other");
 
             var app = MountTestComponent<TestRouter>();
             Assert.Equal("This is another page.", app.FindElement(By.Id("test-info")).Text);
@@ -77,11 +74,11 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         [Fact]
         public void CanFollowLinkToOtherPage()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");
+            SetUrlViaPushState("/");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Other")).Click();
-            Assert.Equal("This is another page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is another page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Other", "Other with base-relative URL (matches all)");
         }
 
@@ -93,20 +90,20 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
 
             try
             {
-                SetUrlViaPushState($"{ServerPathBase}/");
+                SetUrlViaPushState("/");
 
                 var app = MountTestComponent<TestRouter>();
                 var button = app.FindElement(By.LinkText("Other"));
               
                 new Actions(Browser).KeyDown(key).Click(button).Build().Perform();
 
-                Assert.Equal(2, Browser.WindowHandles.Count);
+                WaitAssert.Equal(2, () => Browser.WindowHandles.Count);
             }
             finally
             {
                 // Leaving the ctrl key up 
                 new Actions(Browser).KeyUp(key).Build().Perform();
-                
+
                 // Closing newly opened windows if a new one was opened
                 while (Browser.WindowHandles.Count > 1)
                 {
@@ -123,7 +120,7 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         [Fact]
         public void CanFollowLinkToOtherPageDoesNotOpenNewWindow()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");
+            SetUrlViaPushState("/");
 
             var app = MountTestComponent<TestRouter>();
             
@@ -135,106 +132,106 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
         [Fact]
         public void CanFollowLinkToOtherPageWithBaseRelativeUrl()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");            
+            SetUrlViaPushState("/");            
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Other with base-relative URL (matches all)")).Click();
-            Assert.Equal("This is another page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is another page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Other", "Other with base-relative URL (matches all)");
         }
 
         [Fact]
         public void CanFollowLinkToEmptyStringHrefAsBaseRelativeUrl()
         {
-            SetUrlViaPushState($"{ServerPathBase}/Other");
+            SetUrlViaPushState("/Other");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Default with base-relative URL (matches all)")).Click();
-            Assert.Equal("This is the default page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is the default page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Default (matches all)", "Default with base-relative URL (matches all)");
         }
 
         [Fact]
         public void CanFollowLinkToPageWithParameters()
         {
-            SetUrlViaPushState($"{ServerPathBase}/Other");
+            SetUrlViaPushState("/Other");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("With parameters")).Click();
-            Assert.Equal("Your full name is Abc McDef.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("Your full name is Abc McDef.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("With parameters");
         }
 
         [Fact]
         public void CanFollowLinkToDefaultPage()
         {
-            SetUrlViaPushState($"{ServerPathBase}/Other");
+            SetUrlViaPushState("/Other");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Default (matches all)")).Click();
-            Assert.Equal("This is the default page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is the default page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Default (matches all)", "Default with base-relative URL (matches all)");
         }
 
         [Fact]
         public void CanFollowLinkToOtherPageWithQueryString()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");
+            SetUrlViaPushState("/");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Other with query")).Click();
-            Assert.Equal("This is another page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is another page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Other", "Other with query");
         }
 
         [Fact]
         public void CanFollowLinkToDefaultPageWithQueryString()
         {
-            SetUrlViaPushState($"{ServerPathBase}/Other");
+            SetUrlViaPushState("/Other");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Default with query")).Click();
-            Assert.Equal("This is the default page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is the default page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Default with query");
         }
 
         [Fact]
         public void CanFollowLinkToOtherPageWithHash()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");
+            SetUrlViaPushState("/");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Other with hash")).Click();
-            Assert.Equal("This is another page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is another page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Other", "Other with hash");
         }
 
         [Fact]
         public void CanFollowLinkToDefaultPageWithHash()
         {
-            SetUrlViaPushState($"{ServerPathBase}/Other");
+            SetUrlViaPushState("/Other");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.LinkText("Default with hash")).Click();
-            Assert.Equal("This is the default page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is the default page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Default with hash");
         }
 
         [Fact]
         public void CanNavigateProgrammatically()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");
+            SetUrlViaPushState("/");
 
             var app = MountTestComponent<TestRouter>();
             app.FindElement(By.TagName("button")).Click();
-            Assert.Equal("This is another page.", app.FindElement(By.Id("test-info")).Text);
+            WaitAssert.Equal("This is another page.", () => app.FindElement(By.Id("test-info")).Text);
             AssertHighlightedLinks("Other", "Other with base-relative URL (matches all)");
         }
 
         [Fact]
         public void ClickingAnchorWithNoHrefShouldNotNavigate()
         {
-            SetUrlViaPushState($"{ServerPathBase}/");
+            SetUrlViaPushState("/");
             var initialUrl = Browser.Url;
 
             var app = MountTestComponent<TestRouter>();
@@ -244,25 +241,19 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             AssertHighlightedLinks("Default (matches all)", "Default with base-relative URL (matches all)");
         }
 
-        public void Dispose()
-        {
-            // Clear any existing state
-            SetUrlViaPushState(ServerPathBase);
-            MountTestComponent<TextOnlyComponent>();
-        }
-
         private void SetUrlViaPushState(string relativeUri)
         {
+            var pathBaseWithoutHash = ServerPathBase.Split('#')[0];
             var jsExecutor = (IJavaScriptExecutor)Browser;
-            var absoluteUri = new Uri(_server.RootUri, relativeUri);
+            var absoluteUri = new Uri(_serverFixture.RootUri, $"{pathBaseWithoutHash}{relativeUri}");
             jsExecutor.ExecuteScript($"Blazor.navigateTo('{absoluteUri.ToString().Replace("'", "\\'")}')");
         }
 
         private void AssertHighlightedLinks(params string[] linkTexts)
         {
-            var actual = Browser.FindElements(By.CssSelector("a.active"));
+            WaitAssert.Equal(linkTexts, () => Browser
-            var actualTexts = actual.Select(x => x.Text);
+                .FindElements(By.CssSelector("a.active"))
-            Assert.Equal(linkTexts, actualTexts);
+                .Select(x => x.Text));
         }
     }
 }

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/StandaloneAppTest.cs

@@ -15,15 +15,12 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
     public class StandaloneAppTest
         : ServerTestBase<DevHostServerFixture<StandaloneApp.Program>>, IDisposable
     {
-        private readonly ServerFixture _serverFixture;
-
         public StandaloneAppTest(
             BrowserFixture browserFixture, 
             DevHostServerFixture<StandaloneApp.Program> serverFixture,
             ITestOutputHelper output)
             : base(browserFixture, serverFixture, output)
         {
-            _serverFixture = serverFixture;
             Navigate("/", noReload: true);
             WaitUntilLoaded();
         }

test/testapps/BasicTestApp/CounterComponent.cshtml

@@ -1,4 +1,4 @@
-<h1>Counter</h1>
+<h1>Counter</h1>
 <p>Current count: @currentCount</p>
 <p><button onclick="@((handleClicks ? (Action)IncrementCount : null))">Click me</button></p>
 
@@ -7,6 +7,11 @@
     Toggle click handler registration
 </label>
 
+@if (handleClicks)
+{
+    <p id="listening-message">Listening</p>
+}
+
 @functions {
     int currentCount = 0;
     bool handleClicks = true;

test/testapps/BasicTestApp/Index.cshtml

@@ -0,0 +1,64 @@
+@using Microsoft.AspNetCore.Blazor.RenderTree
+<div id="test-selector">
+  Select test:
+  <select bind=@SelectedComponentTypeName>
+    <option value="none">Choose...</option>
+    <option value="BasicTestApp.InteropComponent">Interop component</option>
+    <option value="BasicTestApp.AsyncEventHandlerComponent">Async event handlers</option>
+    <option value="BasicTestApp.AddRemoveChildComponents">Add/remove child components</option>
+    <option value="BasicTestApp.CounterComponent">Counter</option>
+    <option value="BasicTestApp.CounterComponentUsingChild">Counter using child component</option>
+    <option value="BasicTestApp.CounterComponentWrapper">Counter wrapped in parent</option>
+    <option value="BasicTestApp.FocusEventComponent">Focus events</option>
+    <option value="BasicTestApp.KeyPressEventComponent">Key press event</option>
+    <option value="BasicTestApp.MouseEventComponent">Mouse events</option>
+    <option value="BasicTestApp.TouchEventComponent">Touch events</option>
+    <option value="BasicTestApp.ParentChildComponent">Parent component with child</option>
+    <option value="BasicTestApp.PropertiesChangedHandlerParent">Parent component that changes parameters on child</option>
+    <option value="BasicTestApp.RedTextComponent">Red text</option>
+    <option value="BasicTestApp.RenderFragmentToggler">Render fragment renderer</option>
+    <option value="BasicTestApp.TextOnlyComponent">Plain text</option>
+    <option value="BasicTestApp.HierarchicalImportsTest.Subdir.ComponentUsingImports">Imports statement</option>
+    <option value="BasicTestApp.HttpClientTest.HttpRequestsComponent">HttpClient tester</option>
+    <option value="BasicTestApp.HttpClientTest.BinaryHttpRequestsComponent">Binary HttpClient tester</option>
+    <option value="BasicTestApp.HttpClientTest.CookieCounterComponent">HttpClient cookies</option>
+    <option value="BasicTestApp.BindCasesComponent">bind cases</option>
+    <option value="BasicTestApp.DataDashComponent">data-* attribute rendering</option>
+    <option value="BasicTestApp.ExternalContentPackage">External content package</option>
+    <option value="BasicTestApp.SvgComponent">SVG</option>
+    <option value="BasicTestApp.SvgWithChildComponent">SVG with child component</option>
+    <option value="BasicTestApp.LogicalElementInsertionCases">Logical element insertion cases</option>
+    <option value="BasicTestApp.ElementRefComponent">Element ref component</option>
+    <option value="BasicTestApp.ComponentRefComponent">Component ref component</option>
+    <option value="BasicTestApp.AfterRenderInteropComponent">After-render interop component</option>
+    <option value="BasicTestApp.EventCasesComponent">Event cases</option>
+    <option value="BasicTestApp.EventBubblingComponent">Event bubbling</option>
+    <option value="BasicTestApp.RouterTest.TestRouter">Router</option>
+  </select>
+
+  @if (SelectedComponentType != null)
+  {
+    <span id="source-info"><code><tt>@(SelectedComponentType.Name.Replace(".", "/")).cshtml</tt></code></span>
+  }
+  <hr />
+</div>
+
+<app>
+    @((RenderFragment)RenderSelectedComponent)
+</app>
+
+@functions {
+    string SelectedComponentTypeName { get; set; } = "none";
+
+    Type SelectedComponentType
+        => SelectedComponentTypeName == "none" ? null : Type.GetType(SelectedComponentTypeName);
+
+    void RenderSelectedComponent(RenderTreeBuilder builder)
+    {
+        if (SelectedComponentType != null)
+        {
+            builder.OpenComponent(0, SelectedComponentType);
+            builder.CloseComponent();
+        }
+    }
+}

test/testapps/BasicTestApp/InteropComponent.cshtml

@@ -1,5 +1,6 @@
 @using Microsoft.JSInterop
 @using BasicTestApp.InteropTest
+@using System.Runtime.InteropServices
 
 <button id="btn-interop" onclick="@InvokeInteropAsync">Invoke interop!</button>
 
@@ -65,18 +66,24 @@
 
     public async Task InvokeInteropAsync()
     {
-        var inProcRuntime = ((IJSInProcessRuntime)JSRuntime.Current);
+        var shouldSupportSyncInterop = RuntimeInformation.IsOSPlatform(OSPlatform.Create("WEBASSEMBLY"));
         var testDTOTOPassByRef = new TestDTO(nonSerializedValue: 123);
-
         var instanceMethodsTarget = new JavaScriptInterop();
 
         Console.WriteLine("Starting interop invocations.");
         await JSRuntime.Current.InvokeAsync<object>(
             "jsInteropTests.invokeDotNetInteropMethodsAsync",
+            shouldSupportSyncInterop,
             new DotNetObjectRef(testDTOTOPassByRef),
             new DotNetObjectRef(instanceMethodsTarget));
+
+        if (shouldSupportSyncInterop)
+        {
+            InvokeInProcessInterop();
+        }
+
         Console.WriteLine("Showing interop invocation results.");
-        var collectResults = inProcRuntime.Invoke<Dictionary<string,string>>("jsInteropTests.collectInteropResults");
+        var collectResults = await JSRuntime.Current.InvokeAsync<Dictionary<string,string>>("jsInteropTests.collectInteropResults");
 
         ReturnValues = collectResults.ToDictionary(kvp => kvp.Key,kvp => System.Text.Encoding.UTF8.GetString(Convert.FromBase64String(kvp.Value)));
 
@@ -87,15 +94,6 @@
             invocations[interopResult.Key] = interopResultValue;
         }
 
-        try
-        {
-            inProcRuntime.Invoke<object>("jsInteropTests.functionThrowsException");
-        }
-        catch (JSException e)
-        {
-            ExceptionFromSyncMethod = e;
-        }
-
         try
         {
             await JSRuntime.Current.InvokeAsync<object>("jsInteropTests.asyncFunctionThrowsSyncException");
@@ -120,15 +118,39 @@
             { "stringValue", "My string" },
             { "testDto", new DotNetObjectRef(passDotNetObjectByRef) },
         };
-        ReceiveDotNetObjectByRefResult = inProcRuntime.Invoke<Dictionary<string, object>>("receiveDotNetObjectByRef", passDotNetObjectByRefArg);
         ReceiveDotNetObjectByRefAsyncResult = await JSRuntime.Current.InvokeAsync<Dictionary<string, object>>("receiveDotNetObjectByRefAsync", passDotNetObjectByRefArg);
-        ReceiveDotNetObjectByRefResult["testDto"] = ReceiveDotNetObjectByRefResult["testDto"] == passDotNetObjectByRef ? "Same" : "Different";
         ReceiveDotNetObjectByRefAsyncResult["testDto"] = ReceiveDotNetObjectByRefAsyncResult["testDto"] == passDotNetObjectByRef ? "Same" : "Different";
 
-        ReturnValues["returnPrimitive"] = inProcRuntime.Invoke<int>("returnPrimitive").ToString();
         ReturnValues["returnPrimitiveAsync"] = (await JSRuntime.Current.InvokeAsync<int>("returnPrimitiveAsync")).ToString();
+        if (shouldSupportSyncInterop)
+        {
+            ReturnValues["returnPrimitive"] = ((IJSInProcessRuntime)JSRuntime.Current).Invoke<int>("returnPrimitive").ToString();
+        }
 
         Invocations = invocations;
         DoneWithInterop = true;
     }
+
+    public void InvokeInProcessInterop()
+    {
+        var inProcRuntime = ((IJSInProcessRuntime)JSRuntime.Current);
+
+        try
+        {
+            inProcRuntime.Invoke<object>("jsInteropTests.functionThrowsException");
+        }
+        catch (JSException e)
+        {
+            ExceptionFromSyncMethod = e;
+        }
+
+        var passDotNetObjectByRef = new TestDTO(99999);
+        var passDotNetObjectByRefArg = new Dictionary<string, object>
+        {
+            { "stringValue", "My string" },
+            { "testDto", new DotNetObjectRef(passDotNetObjectByRef) },
+        };
+        ReceiveDotNetObjectByRefResult = inProcRuntime.Invoke<Dictionary<string, object>>("receiveDotNetObjectByRef", passDotNetObjectByRefArg);
+        ReceiveDotNetObjectByRefResult["testDto"] = ReceiveDotNetObjectByRefResult["testDto"] == passDotNetObjectByRef ? "Same" : "Different";
+    }
 }

test/testapps/BasicTestApp/Program.cs

@@ -1,32 +1,19 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.AspNetCore.Blazor.Browser.Http;
+using Microsoft.AspNetCore.Blazor.Hosting;
-using Microsoft.AspNetCore.Blazor.Browser.Rendering;
-using Microsoft.AspNetCore.Blazor.Browser.Services;
-using Microsoft.JSInterop;
-using System;
 
 namespace BasicTestApp
 {
     public class Program
     {
-        static void Main(string[] args)
+        public static void Main(string[] args)
         {
-            // Needed because the test server runs on a different port than the client app,
+            CreateHostBuilder(args).Build().Run();
-            // and we want to test sending/receiving cookies undering this config
-            BrowserHttpMessageHandler.DefaultCredentials = FetchCredentialsOption.Include;
-
-            // Signal to tests that we're ready
-            GC.KeepAlive(ActivateMonoJSRuntime.EnsureActivated());
-            JSRuntime.Current.InvokeAsync<object>("testReady");
         }
 
-        [JSInvokable(nameof(MountTestComponent))]
+        public static IWebAssemblyHostBuilder CreateHostBuilder(string[] args) =>
-        public static void MountTestComponent(string componentTypeName)
+            BlazorWebAssemblyHost.CreateDefaultBuilder()
-        {
+                .UseBlazorStartup<Startup>();
-            var componentType = Type.GetType(componentTypeName);
-            new BrowserRenderer().AddComponent(componentType, "app");
-        }
     }
 }

test/testapps/BasicTestApp/Startup.cs

@@ -0,0 +1,33 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Blazor.Browser.Http;
+using Microsoft.AspNetCore.Blazor.Browser.Services;
+using Microsoft.AspNetCore.Blazor.Builder;
+using Microsoft.Extensions.DependencyInjection;
+using System;
+using System.Runtime.InteropServices;
+
+namespace BasicTestApp
+{
+    public class Startup
+    {
+        public void ConfigureServices(IServiceCollection services)
+        {
+        }
+
+        public void Configure(IBlazorApplicationBuilder app)
+        {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Create("WEBASSEMBLY")))
+            {
+                // Needed because the test server runs on a different port than the client app,
+                // and we want to test sending/receiving cookies undering this config
+                BrowserHttpMessageHandler.DefaultCredentials = FetchCredentialsOption.Include;
+
+                GC.KeepAlive(ActivateMonoJSRuntime.EnsureActivated());
+            }
+
+            app.AddComponent<Index>("root");
+        }
+    }
+}

test/testapps/BasicTestApp/wwwroot/index.html

@@ -6,71 +6,26 @@
     <base href="/subdir/" />
 </head>
 <body>
-  <div id="test-selector" style="display: none;">
+  <root>Loading...</root>
-    Select test:
-    <select onchange="mountTestComponent(event.target.value)">
-      <option value="">Choose...</option>
-      <option value="BasicTestApp.InteropComponent">Interop component</option>
-      <option value="BasicTestApp.AsyncEventHandlerComponent">Async event handlers</option>
-      <option value="BasicTestApp.AddRemoveChildComponents">Add/remove child components</option>
-      <option value="BasicTestApp.CounterComponent">Counter</option>
-      <option value="BasicTestApp.CounterComponentUsingChild">Counter using child component</option>
-      <option value="BasicTestApp.CounterComponentWrapper">Counter wrapped in parent</option>
-      <option value="BasicTestApp.FocusEventComponent">Focus events</option>
-      <option value="BasicTestApp.KeyPressEventComponent">Key press event</option>
-      <option value="BasicTestApp.MouseEventComponent">Mouse events</option>
-      <option value="BasicTestApp.TouchEventComponent">Touch events</option>
-      <option value="BasicTestApp.ParentChildComponent">Parent component with child</option>
-      <option value="BasicTestApp.PropertiesChangedHandlerParent">Parent component that changes parameters on child</option>
-      <option value="BasicTestApp.RedTextComponent">Red text</option>
-      <option value="BasicTestApp.RenderFragmentToggler">Render fragment renderer</option>
-      <option value="BasicTestApp.TextOnlyComponent">Plain text</option>
-      <option value="BasicTestApp.HierarchicalImportsTest.Subdir.ComponentUsingImports">Imports statement</option>
-      <option value="BasicTestApp.HttpClientTest.HttpRequestsComponent">HttpClient tester</option>
-      <option value="BasicTestApp.HttpClientTest.BinaryHttpRequestsComponent">Binary HttpClient tester</option>
-      <option value="BasicTestApp.HttpClientTest.CookieCounterComponent">HttpClient cookies</option>
-      <option value="BasicTestApp.BindCasesComponent">@bind cases</option>
-      <option value="BasicTestApp.ExternalContentPackage">External content package</option>
-      <option value="BasicTestApp.SvgComponent">SVG</option>
-      <option value="BasicTestApp.SvgWithChildComponent">SVG with child component</option>
-      <option value="BasicTestApp.LogicalElementInsertionCases">Logical element insertion cases</option>
-      <option value="BasicTestApp.ElementRefComponent">Element ref component</option>
-      <option value="BasicTestApp.ComponentRefComponent">Component ref component</option>
-      <option value="BasicTestApp.AfterRenderInteropComponent">After-render interop component</option>
-      <option value="BasicTestApp.EventCasesComponent">Event cases</option>
-      <!--<option value="BasicTestApp.RouterTest.Default">Router</option> Excluded because it requires additional setup to work correctly when loaded manually -->
-    </select>
-    &nbsp;
-    <span id="source-info"></span>
-    <hr />
-  </div>
-
-  <app>Loading...</app>
-
-  <script src="_framework/blazor.webassembly.js"></script>
 
   <!-- Used for testing interop scenarios between JS and .NET -->
   <script src="js/jsinteroptests.js"></script>
 
   <script>
-    // The client-side .NET code calls this when it is ready to be called from test code
-    // The Xunit test code polls until it sees the flag is set
-    function testReady() {
-      window.isTestReady = true;
-      document.getElementsByTagName('APP')[0].textContent = '';
-      document.getElementById('test-selector').style.display = 'block';
-    }
-
-    // The Xunit test code calls this when setting up tests for specific components
-    function mountTestComponent(typeName) {
-      document.getElementById('source-info').innerHTML = '<code><tt>' + typeName.replace(/\./g, '/') + '.cshtml</code></strong>';
-      DotNet.invokeMethodAsync('BasicTestApp', 'MountTestComponent', typeName);
-    }
-
     // Used by ElementRefComponent
     function setElementValue(element, newValue) {
       element.value = newValue;
     }
+
+    (function () {
+      // Load either blazor.webassembly.js or blazor.server.js depending
+      // on the hash part of the URL. This is just to give a way for the
+      // test runner to make the selection.
+      var src = location.hash === '#server'
+        ? 'blazor.server.js'
+        : 'blazor.webassembly.js';
+      document.write('<script src="_framework/' + src + '"><' + '/script>');
+    })();
   </script>
 </body>
 </html>

test/testapps/BasicTestApp/wwwroot/js/jsinteroptests.js

@@ -4,40 +4,42 @@
 var results = {};
 var assemblyName = 'BasicTestApp';
 
-function invokeDotNetInteropMethodsAsync(dotNetObjectByRef, instanceMethodsTarget) {
+function invokeDotNetInteropMethodsAsync(shouldSupportSyncInterop, dotNetObjectByRef, instanceMethodsTarget) {
-  console.log('Invoking void sync methods.');
+  if (shouldSupportSyncInterop) {
-  DotNet.invokeMethod(assemblyName, 'VoidParameterless');
+    console.log('Invoking void sync methods.');
-  DotNet.invokeMethod(assemblyName, 'VoidWithOneParameter', ...createArgumentList(1, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidParameterless');
-  DotNet.invokeMethod(assemblyName, 'VoidWithTwoParameters', ...createArgumentList(2, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithOneParameter', ...createArgumentList(1, dotNetObjectByRef));
-  DotNet.invokeMethod(assemblyName, 'VoidWithThreeParameters', ...createArgumentList(3, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithTwoParameters', ...createArgumentList(2, dotNetObjectByRef));
-  DotNet.invokeMethod(assemblyName, 'VoidWithFourParameters', ...createArgumentList(4, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithThreeParameters', ...createArgumentList(3, dotNetObjectByRef));
-  DotNet.invokeMethod(assemblyName, 'VoidWithFiveParameters', ...createArgumentList(5, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithFourParameters', ...createArgumentList(4, dotNetObjectByRef));
-  DotNet.invokeMethod(assemblyName, 'VoidWithSixParameters', ...createArgumentList(6, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithFiveParameters', ...createArgumentList(5, dotNetObjectByRef));
-  DotNet.invokeMethod(assemblyName, 'VoidWithSevenParameters', ...createArgumentList(7, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithSixParameters', ...createArgumentList(6, dotNetObjectByRef));
-  DotNet.invokeMethod(assemblyName, 'VoidWithEightParameters', ...createArgumentList(8, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithSevenParameters', ...createArgumentList(7, dotNetObjectByRef));
+    DotNet.invokeMethod(assemblyName, 'VoidWithEightParameters', ...createArgumentList(8, dotNetObjectByRef));
 
-  console.log('Invoking returning sync methods.');
+    console.log('Invoking returning sync methods.');
-  results['result1'] = DotNet.invokeMethod(assemblyName, 'ReturnArray');
+    results['result1'] = DotNet.invokeMethod(assemblyName, 'ReturnArray');
-  results['result2'] = DotNet.invokeMethod(assemblyName, 'EchoOneParameter', ...createArgumentList(1, dotNetObjectByRef));
+    results['result2'] = DotNet.invokeMethod(assemblyName, 'EchoOneParameter', ...createArgumentList(1, dotNetObjectByRef));
-  results['result3'] = DotNet.invokeMethod(assemblyName, 'EchoTwoParameters', ...createArgumentList(2, dotNetObjectByRef));
+    results['result3'] = DotNet.invokeMethod(assemblyName, 'EchoTwoParameters', ...createArgumentList(2, dotNetObjectByRef));
-  results['result4'] = DotNet.invokeMethod(assemblyName, 'EchoThreeParameters', ...createArgumentList(3, dotNetObjectByRef));
+    results['result4'] = DotNet.invokeMethod(assemblyName, 'EchoThreeParameters', ...createArgumentList(3, dotNetObjectByRef));
-  results['result5'] = DotNet.invokeMethod(assemblyName, 'EchoFourParameters', ...createArgumentList(4, dotNetObjectByRef));
+    results['result5'] = DotNet.invokeMethod(assemblyName, 'EchoFourParameters', ...createArgumentList(4, dotNetObjectByRef));
-  results['result6'] = DotNet.invokeMethod(assemblyName, 'EchoFiveParameters', ...createArgumentList(5, dotNetObjectByRef));
+    results['result6'] = DotNet.invokeMethod(assemblyName, 'EchoFiveParameters', ...createArgumentList(5, dotNetObjectByRef));
-  results['result7'] = DotNet.invokeMethod(assemblyName, 'EchoSixParameters', ...createArgumentList(6, dotNetObjectByRef));
+    results['result7'] = DotNet.invokeMethod(assemblyName, 'EchoSixParameters', ...createArgumentList(6, dotNetObjectByRef));
-  results['result8'] = DotNet.invokeMethod(assemblyName, 'EchoSevenParameters', ...createArgumentList(7, dotNetObjectByRef));
+    results['result8'] = DotNet.invokeMethod(assemblyName, 'EchoSevenParameters', ...createArgumentList(7, dotNetObjectByRef));
-  results['result9'] = DotNet.invokeMethod(assemblyName, 'EchoEightParameters', ...createArgumentList(8, dotNetObjectByRef));
+    results['result9'] = DotNet.invokeMethod(assemblyName, 'EchoEightParameters', ...createArgumentList(8, dotNetObjectByRef));
 
-  var returnDotNetObjectByRefResult = DotNet.invokeMethod(assemblyName, 'ReturnDotNetObjectByRef');
+    var returnDotNetObjectByRefResult = DotNet.invokeMethod(assemblyName, 'ReturnDotNetObjectByRef');
-  results['resultReturnDotNetObjectByRefSync'] = DotNet.invokeMethod(assemblyName, 'ExtractNonSerializedValue', returnDotNetObjectByRefResult['Some sync instance']);
+    results['resultReturnDotNetObjectByRefSync'] = DotNet.invokeMethod(assemblyName, 'ExtractNonSerializedValue', returnDotNetObjectByRefResult['Some sync instance']);
 
-  var instanceMethodResult = instanceMethodsTarget.invokeMethod('InstanceMethod', {
+    var instanceMethodResult = instanceMethodsTarget.invokeMethod('InstanceMethod', {
-    stringValue: 'My string',
+      stringValue: 'My string',
-    dtoByRef: dotNetObjectByRef
+      dtoByRef: dotNetObjectByRef
-  });
+    });
-  results['instanceMethodThisTypeName'] = instanceMethodResult.thisTypeName;
+    results['instanceMethodThisTypeName'] = instanceMethodResult.thisTypeName;
-  results['instanceMethodStringValueUpper'] = instanceMethodResult.stringValueUpper;
+    results['instanceMethodStringValueUpper'] = instanceMethodResult.stringValueUpper;
-  results['instanceMethodIncomingByRef'] = instanceMethodResult.incomingByRef;
+    results['instanceMethodIncomingByRef'] = instanceMethodResult.incomingByRef;
-  results['instanceMethodOutgoingByRef'] = DotNet.invokeMethod(assemblyName, 'ExtractNonSerializedValue', instanceMethodResult.outgoingByRef);
+    results['instanceMethodOutgoingByRef'] = DotNet.invokeMethod(assemblyName, 'ExtractNonSerializedValue', instanceMethodResult.outgoingByRef);
+  }
 
   console.log('Invoking void async methods.');
   return DotNet.invokeMethodAsync(assemblyName, 'VoidParameterlessAsync')
@@ -70,8 +72,9 @@ function invokeDotNetInteropMethodsAsync(dotNetObjectByRef, instanceMethodsTarge
         .then(() => DotNet.invokeMethodAsync(assemblyName, 'EchoEightParametersAsync', ...createArgumentList(8, dotNetObjectByRef)))
         .then(r => results['result9Async'] = r)
         .then(() => DotNet.invokeMethodAsync(assemblyName, 'ReturnDotNetObjectByRefAsync'))
+        .then(r => DotNet.invokeMethodAsync(assemblyName, 'ExtractNonSerializedValue', r['Some async instance']))
         .then(r => {
-          results['resultReturnDotNetObjectByRefAsync'] = DotNet.invokeMethod(assemblyName, 'ExtractNonSerializedValue', r['Some async instance']);
+          results['resultReturnDotNetObjectByRefAsync'] = r;
         })
         .then(() => instanceMethodsTarget.invokeMethodAsync('InstanceMethodAsync', {
           stringValue: 'My string',
@@ -81,13 +84,15 @@ function invokeDotNetInteropMethodsAsync(dotNetObjectByRef, instanceMethodsTarge
           results['instanceMethodThisTypeNameAsync'] = r.thisTypeName;
           results['instanceMethodStringValueUpperAsync'] = r.stringValueUpper;
           results['instanceMethodIncomingByRefAsync'] = r.incomingByRef;
-          results['instanceMethodOutgoingByRefAsync'] = DotNet.invokeMethod(assemblyName, 'ExtractNonSerializedValue', r.outgoingByRef);
+          return DotNet.invokeMethodAsync(assemblyName, 'ExtractNonSerializedValue', r.outgoingByRef);
+        }).then(r => {
+          results['instanceMethodOutgoingByRefAsync'] = r;
         })
     })
     .then(() => {
       console.log('Invoking methods that throw exceptions');
       try {
-        DotNet.invokeMethod(assemblyName, 'ThrowException');
+        shouldSupportSyncInterop && DotNet.invokeMethod(assemblyName, 'ThrowException');
       } catch (e) {
         results['ThrowException'] = e.message;
       }
@@ -224,10 +229,18 @@ function receiveDotNetObjectByRef(incomingData) {
 }
 
 function receiveDotNetObjectByRefAsync(incomingData) {
-  return new Promise(function (resolve, reject) {
+  const stringValue = incomingData.stringValue;
-    setTimeout(function () {
+  const testDto = incomingData.testDto;
-      const promiseResult = receiveDotNetObjectByRef(incomingData);
+
-      resolve(promiseResult);
+  // To verify we received a proper reference to testDto, pass it back into .NET
-    }, 100);
+  // to have it evaluate something that only .NET can know
+  return DotNet.invokeMethodAsync(assemblyName, 'ExtractNonSerializedValue', testDto).then(testDtoNonSerializedValue => {
+    // To show we can return a .NET object by ref anywhere in a complex structure,
+    // return it among other values
+    return {
+      stringValueUpper: stringValue.toUpperCase(),
+      testDtoNonSerializedValue: testDtoNonSerializedValue,
+      testDto: testDto
+    };
   });
 }

test/testapps/TestServer/Startup.cs

@@ -1,4 +1,4 @@
-using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -22,6 +22,7 @@ namespace TestServer
             {
                 options.AddPolicy("AllowAll", _ => { /* Controlled below */ });
             });
+            services.AddServerSideBlazor<BasicTestApp.Startup>();
         }
 
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
@@ -34,6 +35,12 @@ namespace TestServer
 
             AllowCorsForAnyLocalhostPort(app);
             app.UseMvc();
+
+            // Mount the server-side Blazor app on /subdir
+            app.Map("/subdir", subdirApp =>
+            {
+                subdirApp.UseServerSideBlazor<BasicTestApp.Startup>();
+            });
         }
 
         private static void AllowCorsForAnyLocalhostPort(IApplicationBuilder app)

test/testapps/TestServer/TestServer.csproj

@@ -7,4 +7,9 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.App" Version="$(AspNetCorePackageVersion)" />
   </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\src\Microsoft.AspNetCore.Blazor.Server\Microsoft.AspNetCore.Blazor.Server.csproj" />
+    <ProjectReference Include="..\BasicTestApp\BasicTestApp.csproj" />
+  </ItemGroup>
 </Project>