add unit test for Temporary Storage preserving SourceText Encoding

src/Workspaces/CoreTest/WorkspaceServiceTests/TemporaryStorageServiceTests.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Host;
@@ -323,5 +324,24 @@ public void StreamTest3()
                 }
             }
         }
+
+        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/353"), Trait(Traits.Feature, Traits.Features.Workspace)]
+        public void TestTemporaryStorageTextEncoding()
+        {
+            var textFactory = new TextFactoryService();
+            var service = new TemporaryStorageServiceFactory.TemporaryStorageService(textFactory);
+
+            // test normal string
+            var text = SourceText.From(new string(' ', 4096) + "public class A {}", Encoding.ASCII);
+            TestTemporaryStorage(service, text);
+
+            // test empty string
+            text = SourceText.From(string.Empty);
+            TestTemporaryStorage(service, text);
+
+            // test large string
+            text = SourceText.From(new string(' ', 1024 * 1024) + "public class A {}");
+            TestTemporaryStorage(service, text);
+        }
     }
 }