#1256 Check HasStarted for StatusCode and ReasonPhrase

src/Microsoft.AspNetCore.TestHost/ResponseFeature.cs

@@ -14,6 +14,8 @@ namespace Microsoft.AspNetCore.TestHost
         private Func<Task> _responseStartingAsync = () => Task.FromResult(true);
         private Func<Task> _responseCompletedAsync = () => Task.FromResult(true);
         private HeaderDictionary _headers = new HeaderDictionary();
+        private int _statusCode;
+        private string _reasonPhrase;
 
         public ResponseFeature()
         {
@@ -25,9 +27,37 @@ namespace Microsoft.AspNetCore.TestHost
             StatusCode = 200;
         }
 
-        public int StatusCode { get; set; }
+        public int StatusCode
+        {
+            get => _statusCode;
+            set
+            {
+                if (HasStarted)
+                {
+                    throw new InvalidOperationException("The status code cannot be set, the response has already started.");
+                }
+                if (value < 100)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(value), value, "The status code cannot be set to a value less than 100");
+                }
 
-        public string ReasonPhrase { get; set; }
+                _statusCode = value;
+            }
+        }
+
+        public string ReasonPhrase
+        {
+            get => _reasonPhrase;
+            set
+            {
+                if (HasStarted)
+                {
+                    throw new InvalidOperationException("The reason phrase cannot be set, the response has already started.");
+                }
+
+                _reasonPhrase = value;
+            }
+        }
 
         public IHeaderDictionary Headers { get; set; }
 

test/Microsoft.AspNetCore.TestHost.Tests/ResponseFeatureTests.cs

@@ -41,5 +41,28 @@ namespace Microsoft.AspNetCore.TestHost
                 }, state: "string");
             });
         }
+
+        [Fact]
+        public void StatusCode_ThrowsWhenHasStarted()
+        {
+            var responseInformation = new ResponseFeature();
+            responseInformation.HasStarted = true;
+
+            Assert.Throws<InvalidOperationException>(() => responseInformation.StatusCode = 400);
+            Assert.Throws<InvalidOperationException>(() => responseInformation.ReasonPhrase = "Hello World");
+        }
+
+        [Fact]
+        public void StatusCode_MustBeGreaterThan99()
+        {
+            var responseInformation = new ResponseFeature();
+
+            Assert.Throws<ArgumentOutOfRangeException>(() => responseInformation.StatusCode = 99);
+            Assert.Throws<ArgumentOutOfRangeException>(() => responseInformation.StatusCode = 0);
+            Assert.Throws<ArgumentOutOfRangeException>(() => responseInformation.StatusCode = -200);
+            responseInformation.StatusCode = 100;
+            responseInformation.StatusCode = 200;
+            responseInformation.StatusCode = 1000;
+        }
     }
 }