Merge pull request #558 from dotnet/dev/phil-allen-msft/xunitFixes

Update Xunit usage to use Assert.Fail

src/Microsoft.DiaSymReader.PortablePdb.Tests/TestHelpers/AssertEx.cs

@@ -203,7 +203,7 @@ namespace Roslyn.Test.Utilities
                     assertMessage = message + "\r\n" + assertMessage;
                 }
 
-                Assert.True(false, assertMessage);
+                Assert.Fail(assertMessage);
             }
         }
 
@@ -306,12 +306,12 @@ namespace Roslyn.Test.Utilities
 
         public static void Fail(string message)
         {
-            Assert.False(true, message);
+            Assert.Fail(message);
         }
 
         public static void Fail(string format, params object[] args)
         {
-            Assert.False(true, string.Format(format, args));
+            Assert.Fail(string.Format(format, args));
         }
 
         public static void Null<T>(T @object, string message = null)