How about this?

test/Microsoft.AspNetCore.SignalR.Client.FunctionalTests/HubConnectionTests.cs

@@ -30,7 +30,7 @@ namespace Microsoft.AspNetCore.SignalR.Client.FunctionalTests
     }
 
     [Collection(HubConnectionTestsCollection.Name)]
-    public class HubConnectionTests : VerifiableServerLoggedTest<Startup>
+    public class HubConnectionTests : VerifiableServerLoggedTest
     {
         private readonly ServerFixture<Startup> _serverFixture;
         public HubConnectionTests(ServerFixture<Startup> serverFixture, ITestOutputHelper output) : base(serverFixture, output)

test/Microsoft.AspNetCore.SignalR.Tests.Utils/ServerFixture.cs

@@ -18,7 +18,18 @@ using Microsoft.Extensions.Logging.Testing;
 
 namespace Microsoft.AspNetCore.SignalR.Tests
 {
-    public class ServerFixture<TStartup> : IDisposable
+    public abstract class ServerFixture : IDisposable
+    {
+        internal abstract event Action<LogRecord> ServerLogged;
+
+        public abstract string WebSocketsUrl { get; }
+
+        public abstract string Url { get; }
+
+        public abstract void Dispose();
+    }
+
+    public class ServerFixture<TStartup> : ServerFixture
         where TStartup : class
     {
         private readonly ILoggerFactory _loggerFactory;
@@ -28,16 +39,17 @@ namespace Microsoft.AspNetCore.SignalR.Tests
         private readonly IDisposable _logToken;
 
         private readonly LogSinkProvider _logSinkProvider;
+        private string _url;
 
-        internal event Action<LogRecord> ServerLogged
+        internal override event Action<LogRecord> ServerLogged
         {
             add => _logSinkProvider.RecordLogged += value;
             remove => _logSinkProvider.RecordLogged -= value;
         }
 
-        public string WebSocketsUrl => Url.Replace("http", "ws");
+        public override string WebSocketsUrl => Url.Replace("http", "ws");
 
-        public string Url { get; private set; }
+        public override string Url => _url;
 
         public ServerFixture() : this(loggerFactory: null)
         {
@@ -98,7 +110,7 @@ namespace Microsoft.AspNetCore.SignalR.Tests
             _logger.LogInformation("Test Server started");
 
             // Get the URL from the server
-            Url = _host.ServerFeatures.Get<IServerAddressesFeature>().Addresses.Single();
+            _url = _host.ServerFeatures.Get<IServerAddressesFeature>().Addresses.Single();
 
             _lifetime.ApplicationStopped.Register(() =>
             {
@@ -125,7 +137,7 @@ namespace Microsoft.AspNetCore.SignalR.Tests
             return builder.ToString();
         }
 
-        public void Dispose()
+        public override void Dispose()
         {
             _logger.LogInformation("Shutting down test server");
             _host.Dispose();

test/Microsoft.AspNetCore.SignalR.Tests.Utils/ServerLogScope.cs

@@ -6,13 +6,13 @@ using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.SignalR.Tests
 {
-    public class ServerLogScope<TStartup> : IDisposable where TStartup : class
+    public class ServerLogScope : IDisposable
     {
-        private readonly ServerFixture<TStartup> _serverFixture;
+        private readonly ServerFixture _serverFixture;
         private readonly IDisposable _wrappedDisposable;
         //private readonly ILogger _logger;
 
-        public ServerLogScope(ServerFixture<TStartup> serverFixture, ILoggerFactory loggerFactory, IDisposable wrappedDisposable)
+        public ServerLogScope(ServerFixture serverFixture, ILoggerFactory loggerFactory, IDisposable wrappedDisposable)
         {
             _serverFixture = serverFixture;
             _wrappedDisposable = wrappedDisposable;

test/Microsoft.AspNetCore.SignalR.Tests.Utils/VerifiableServerLoggedTest.cs

@@ -8,11 +8,11 @@ using Xunit.Abstractions;
 
 namespace Microsoft.AspNetCore.SignalR.Tests
 {
-    public class VerifiableServerLoggedTest<TStartup> : VerifiableLoggedTest where TStartup : class 
+    public class VerifiableServerLoggedTest : VerifiableLoggedTest
     {
-        public ServerFixture<TStartup> ServerFixture { get; }
+        public ServerFixture ServerFixture { get; }
 
-        public VerifiableServerLoggedTest(ServerFixture<TStartup> serverFixture, ITestOutputHelper output) : base(output)
+        public VerifiableServerLoggedTest(ServerFixture serverFixture, ITestOutputHelper output) : base(output)
         {
             ServerFixture = serverFixture;
         }
@@ -20,13 +20,13 @@ namespace Microsoft.AspNetCore.SignalR.Tests
         public override IDisposable StartVerifableLog(out ILoggerFactory loggerFactory, LogLevel minLogLevel, string testName = null, Func<WriteContext, bool> expectedErrorsFilter = null)
         {
             var disposable = base.StartVerifableLog(out loggerFactory, minLogLevel, testName, expectedErrorsFilter);
-            return new ServerLogScope<TStartup>(ServerFixture, loggerFactory, disposable);
+            return new ServerLogScope(ServerFixture, loggerFactory, disposable);
         }
 
         public override IDisposable StartVerifableLog(out ILoggerFactory loggerFactory, string testName = null, Func<WriteContext, bool> expectedErrorsFilter = null)
         {
             var disposable = base.StartVerifableLog(out loggerFactory, testName, expectedErrorsFilter);
-            return new ServerLogScope<TStartup>(ServerFixture, loggerFactory, disposable);
+            return new ServerLogScope(ServerFixture, loggerFactory, disposable);
         }
     }
 }

test/Microsoft.AspNetCore.SignalR.Tests/EndToEndTests.cs

@@ -34,7 +34,7 @@ namespace Microsoft.AspNetCore.SignalR.Tests
     }
 
     [Collection(EndToEndTestsCollection.Name)]
-    public class EndToEndTests : VerifiableServerLoggedTest<Startup>
+    public class EndToEndTests : VerifiableServerLoggedTest
     {
         private readonly ServerFixture<Startup> _serverFixture;
 
@@ -44,6 +44,10 @@ namespace Microsoft.AspNetCore.SignalR.Tests
             {
                 throw new ArgumentNullException(nameof(serverFixture));
             }
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
 
             _serverFixture = serverFixture;
         }

test/Microsoft.AspNetCore.SignalR.Tests/WebSocketsTransportTests.cs

@@ -22,7 +22,7 @@ using Xunit.Abstractions;
 namespace Microsoft.AspNetCore.SignalR.Tests
 {
     [Collection(EndToEndTestsCollection.Name)]
-    public class WebSocketsTransportTests : VerifiableServerLoggedTest<Startup>
+    public class WebSocketsTransportTests : VerifiableServerLoggedTest
     {
         private readonly ServerFixture<Startup> _serverFixture;