Remove TestDocumentMappingService (#10976)

This was only used for a single test and the implementation is trivial
to mock. I noticed this when I saw that `TestDocumentMappingService`
still "implemented" `GetLanguageKind`, which no longer exists on
`IDocumentMappingService`.

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/Delegation/DelegatedCompletionListProvider.cs

@@ -39,7 +39,7 @@ public DelegatedCompletionListProvider(
         IClientConnection clientConnection,
         CompletionListCache completionListCache)
     {
-        _responseRewriters = responseRewriters.OrderBy(rewriter => rewriter.Order).ToImmutableArray();
+        _responseRewriters = responseRewriters.OrderByAsArray(static x => x.Order);
         _documentMappingService = documentMappingService;
         _clientConnection = clientConnection;
         _completionListCache = completionListCache;
@@ -57,7 +57,9 @@ public DelegatedCompletionListProvider(
         Guid correlationId,
         CancellationToken cancellationToken)
     {
-        var positionInfo = await _documentMappingService.GetPositionInfoAsync(documentContext, absoluteIndex, cancellationToken).ConfigureAwait(false);
+        var positionInfo = await _documentMappingService
+            .GetPositionInfoAsync(documentContext, absoluteIndex, cancellationToken)
+            .ConfigureAwait(false);
 
         if (positionInfo.LanguageKind == RazorLanguageKind.Razor)
         {

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Completion/Delegation/DelegatedCompletionListProviderTest.cs

@@ -9,12 +9,15 @@
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.LanguageServer.Hosting;
+using Microsoft.AspNetCore.Razor.Test.Common;
 using Microsoft.AspNetCore.Razor.Test.Common.LanguageServer;
+using Microsoft.CodeAnalysis.Razor.DocumentMapping;
 using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 using Microsoft.CodeAnalysis.Razor.Protocol;
 using Microsoft.CodeAnalysis.Testing;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
+using Moq;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -284,15 +287,16 @@ public async Task ShouldIncludeSnippets(string input, bool shouldIncludeSnippets
         var codeDocument = CreateCodeDocument(code);
         var documentContext = TestDocumentContext.From("C:/path/to/file.cshtml", codeDocument, hostDocumentVersion: 1337);
 
-        var documentMappingService = new TestDocumentMappingService()
-        {
-            LanguageKind = RazorLanguageKind.Html,
-            GeneratedPosition = new LinePosition(0, cursorPosition)
-        };
+        var generatedPosition = new LinePosition(0, cursorPosition);
+
+        var documentMappingServiceMock = new StrictMock<IDocumentMappingService>();
+        documentMappingServiceMock
+            .Setup(x => x.TryMapToGeneratedDocumentPosition(It.IsAny<IRazorGeneratedDocument>(), It.IsAny<int>(), out generatedPosition, out It.Ref<int>.IsAny))
+            .Returns(true);
 
         var completionProvider = new DelegatedCompletionListProvider(
-            Array.Empty<DelegatedCompletionResponseRewriter>(),
-            documentMappingService,
+            responseRewriters: [],
+            documentMappingServiceMock.Object,
             clientConnection,
             new CompletionListCache());