Fix mock

Author: davidwengier

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Formatting_NetFx/FormattingTestBase.cs

@@ -347,6 +347,9 @@ internal static IDocumentSnapshot CreateDocumentSnapshot(
                 return CreateDocumentSnapshot(
                     path, fileKind, codeDocument, projectEngine, imports, importDocuments, tagHelpers, inGlobalNamespace);
             });
+        snapshotMock
+            .Setup(d => d.GetCSharpSyntaxTreeAsync(It.IsAny<CancellationToken>()))
+            .ReturnsAsync(codeDocument.GetOrParseCSharpSyntaxTree(CancellationToken.None));
 
         return snapshotMock.Object;
     }