"ConvertTests" rule improvements

This change updates UsesXunitForTestsFormattingRule ("ConvertTests")
to not remove unidentified usings (where the using cannot be mapped
to a symbol because the source of the using may not be in the
workspace), and to remove the ToF "ContractsRequiredAttribute".

Author: Matt Cohn

src/Microsoft.DotNet.CodeFormatting/Rules/UsesXunitForTestsFormattingRule.cs

@@ -52,6 +52,23 @@ public async Task<Solution> ProcessAsync(Document document, SyntaxNode syntaxNod
 
             foreach (var usingSyntax in root.Usings)
             {
+                Action<UsingDirectiveSyntax> addUsing = (UsingDirectiveSyntax newUsingSyntax) =>
+                {
+                    UsingDirectiveSyntax usingDirectiveToUse = newUsingSyntax;
+                    if (usingDirectiveToUse.HasLeadingTrivia)
+                    {
+                        var newLeadingTrivia = RemoveCompilerDirectives(usingDirectiveToUse.GetLeadingTrivia());
+                        usingDirectiveToUse = usingDirectiveToUse.WithLeadingTrivia(newLeadingTrivia);
+                    }
+                    if (usingDirectiveToUse.HasTrailingTrivia)
+                    {
+                        var newTrailingTrivia = RemoveCompilerDirectives(usingDirectiveToUse.GetTrailingTrivia());
+                        usingDirectiveToUse = usingDirectiveToUse.WithTrailingTrivia(newTrailingTrivia);
+                    }
+
+                    newUsings.Add(usingDirectiveToUse);
+                };
+
                 var symbolInfo = semanticModel.GetSymbolInfo(usingSyntax.Name);
                 if (symbolInfo.Symbol != null)
                 {
@@ -62,21 +79,13 @@ public async Task<Solution> ProcessAsync(Document document, SyntaxNode syntaxNod
                     }
                     else
                     {
-                        UsingDirectiveSyntax usingDirectiveToUse = usingSyntax;
-                        if (usingDirectiveToUse.HasLeadingTrivia)
-                        {
-                            var newLeadingTrivia = RemoveCompilerDirectives(usingDirectiveToUse.GetLeadingTrivia());
-                            usingDirectiveToUse = usingDirectiveToUse.WithLeadingTrivia(newLeadingTrivia);
-                        }
-                        if (usingDirectiveToUse.HasTrailingTrivia)
-                        {
-                            var newTrailingTrivia = RemoveCompilerDirectives(usingDirectiveToUse.GetTrailingTrivia());
-                            usingDirectiveToUse = usingDirectiveToUse.WithTrailingTrivia(newTrailingTrivia);
-                        }
-
-                        newUsings.Add(usingDirectiveToUse);
+                        addUsing(usingSyntax);
                     }
                 }
+                else
+                {
+                    addUsing(usingSyntax);
+                }
             }
 
             if (!needsChanges)
@@ -86,6 +95,7 @@ public async Task<Solution> ProcessAsync(Document document, SyntaxNode syntaxNod
 
             TransformationTracker transformationTracker = new TransformationTracker();
             RemoveTestClassAttributes(root, semanticModel, transformationTracker);
+            RemoveContractsRequiredAttributes(root, semanticModel, transformationTracker);
             ChangeTestMethodAttributesToFact(root, semanticModel, transformationTracker);
             ChangeAssertCalls(root, semanticModel, transformationTracker);
             root = transformationTracker.TransformRoot(root);
@@ -115,7 +125,17 @@ public async Task<Solution> ProcessAsync(Document document, SyntaxNode syntaxNod
             return document.WithSyntaxRoot(root).Project.Solution;
         }
 
+        private void RemoveContractsRequiredAttributes(CompilationUnitSyntax root, SemanticModel semanticModel, TransformationTracker transformationTracker)
+        {
+            RemoveTestAttributes(root, semanticModel, transformationTracker, "ContractsRequiredAttribute");
+        }
+
         private void RemoveTestClassAttributes(CompilationUnitSyntax root, SemanticModel semanticModel, TransformationTracker transformationTracker)
+        {
+            RemoveTestAttributes(root, semanticModel, transformationTracker, "TestClassAttribute");
+        }
+
+        private void RemoveTestAttributes(CompilationUnitSyntax root, SemanticModel semanticModel, TransformationTracker transformationTracker, string attributeName)
         {
             List<AttributeSyntax> nodesToRemove = new List<AttributeSyntax>();
 
@@ -127,7 +147,7 @@ private void RemoveTestClassAttributes(CompilationUnitSyntax root, SemanticModel
                     if (typeInfo.Type != null)
                     {
                         string attributeTypeDocID = typeInfo.Type.GetDocumentationCommentId();
-                        if (IsTestNamespaceType(attributeTypeDocID, "TestClassAttribute"))
+                        if (IsTestNamespaceType(attributeTypeDocID, attributeName))
                         {
                             return true;
                         }
@@ -156,6 +176,7 @@ private void RemoveTestClassAttributes(CompilationUnitSyntax root, SemanticModel
                 return transformationRoot;
             });
         }
+
         private void ChangeTestMethodAttributesToFact(CompilationUnitSyntax root, SemanticModel semanticModel, TransformationTracker transformationTracker)
         {
             List<AttributeSyntax> nodesToReplace = new List<AttributeSyntax>();