StatusCodePagesOptions.HandleAsync only includes a semicolon where a reason phrase for the HTTP status is available.

Added Unit Test to cover all HTTP Status Codes from 400 - 599 (inclusive).

src/Microsoft.AspNetCore.Diagnostics/StatusCodePage/StatusCodePagesOptions.cs

@@ -20,15 +20,29 @@ namespace Microsoft.AspNetCore.Builder
             HandleAsync = context =>
             {
                 // TODO: Render with a pre-compiled html razor view.
-                // Note the 500 spaces are to work around an IE 'feature'
                 var statusCode = context.HttpContext.Response.StatusCode;
-                var body = string.Format(CultureInfo.InvariantCulture, "Status Code: {0}; {1}",
-                    statusCode, ReasonPhrases.GetReasonPhrase(statusCode)) + new string(' ', 500);
+
+                var body = BuildResponseBody(statusCode);
+
                 context.HttpContext.Response.ContentType = "text/plain";
                 return context.HttpContext.Response.WriteAsync(body);
             };
         }
 
+        private string BuildResponseBody(int httpStatusCode)
+        {
+            // Note the 500 spaces are to work around an IE 'feature'
+            string internetExplorerWorkaround = new string(' ', 500);
+
+            var reasonPhrase = ReasonPhrases.GetReasonPhrase(httpStatusCode);
+
+            return string.Format(CultureInfo.InvariantCulture, "Status Code: {0}{1}{2}{3}",
+                                                                    httpStatusCode,
+                                                                    string.IsNullOrWhiteSpace(reasonPhrase) ? "" : "; ",
+                                                                    reasonPhrase,
+                                                                    internetExplorerWorkaround);
+        }
+
         public Func<StatusCodeContext, Task> HandleAsync { get; set; }
     }
 }

test/Microsoft.AspNetCore.Diagnostics.FunctionalTests/StatusCodeSampleTest.cs

@@ -1,6 +1,7 @@
 // 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.WebUtilities;
 using System.Net;
 using System.Net.Http;
 using System.Threading.Tasks;
@@ -31,5 +32,45 @@ namespace Microsoft.AspNetCore.Diagnostics.FunctionalTests
             Assert.Equal(HttpStatusCode.OK, response.StatusCode);
             Assert.Contains("Status Code: 417", body);
         }
+
+        [Fact]
+        public async Task StatusCodePageOptions_ExcludesSemicolon_WhenReasonPhrase_IsUnknown()
+        {
+            //Arrange
+            var httpStatusCode = 541;
+            var request = new HttpRequestMessage(HttpMethod.Get, $"http://localhost/?statuscode={httpStatusCode}");
+
+            //Act
+            var response = await Client.SendAsync(request);
+
+            var statusCode = response.StatusCode;
+
+            var responseBody = await response.Content.ReadAsStringAsync();
+
+            //Assert
+            Assert.Equal((HttpStatusCode)httpStatusCode, response.StatusCode);
+            Assert.DoesNotContain(";", responseBody);
+        }   
+
+        [Fact]
+        public async Task StatusCodePageOptions_IncludesSemicolon__AndReasonPhrase_WhenReasonPhrase_IsKnown()
+        {
+            //Arrange    
+            var httpStatusCode = 400;
+            var request = new HttpRequestMessage(HttpMethod.Get, $"http://localhost/?statuscode={httpStatusCode}");
+
+            //Act
+            var response = await Client.SendAsync(request);
+
+            var statusCode = response.StatusCode;
+            var statusCodeReasonPhrase = ReasonPhrases.GetReasonPhrase(httpStatusCode);
+
+            var responseBody = await response.Content.ReadAsStringAsync();
+
+            //Assert
+            Assert.Equal((HttpStatusCode)httpStatusCode, response.StatusCode);
+            Assert.Contains(";", responseBody);
+            Assert.Contains(statusCodeReasonPhrase, responseBody);
+        }
     }
-}
+}