Add more diagnostic information to better understand what's happening if...

Add more diagnostic information to better understand what's happening if TestAddAndRemoveViaTextChangeManyTimes fails

src/VisualStudio/Core/Impl/CodeModel/FileCodeModel.cs

@@ -213,6 +213,8 @@ internal void OnBeforeCodeElementCreated(SyntaxNode node)
             if (!nodeKey.IsEmpty && _codeElementTable.TryGetValue(nodeKey, out codeElement))
             {
                 var managedElement = ComAggregate.GetManagedObject<AbstractKeyedCodeElement>(codeElement);
+                Debug.Assert(managedElement != null, $"Could not get the underlying {nameof(AbstractKeyedCodeElement)} from {nameof(codeElement)} with {nameof(nodeKey)}: {nodeKey}");
+
                 if (managedElement?.IsValidNode() != true)
                 {
                     _codeElementTable.Remove(nodeKey);

src/VisualStudio/Core/Test/CodeModel/CSharp/CodeClassTests.vb

@@ -3845,7 +3845,20 @@ class C$$
             Await TestElement(code,
                 Sub(state, codeClass)
                     For i = 1 To 100
-                        Dim variable = codeClass.AddVariable("x", "System.Int32")
+                        Dim initialDocument = state.FileCodeModelObject.GetDocument()
+                        Dim variable As EnvDTE.CodeVariable
+
+                        Try
+                            variable = codeClass.AddVariable("x", "System.Int32")
+                        Catch ex As InvalidOperationException
+                            Assert.False(True,
+$"Failed to add variable in loop iteration {i}!
+
+Document text:
+{initialDocument.GetTextAsync(CancellationToken.None).Result}")
+
+                            Throw ex
+                        End Try
 
                         ' Now, delete the variable that we just added.
                         Dim startPoint = variable.StartPoint
@@ -3856,7 +3869,7 @@ class C$$
                         document = document.WithText(text)
 
                         Dim result = state.VisualStudioWorkspace.TryApplyChanges(document.Project.Solution)
-                        Assert.True(result)
+                        Assert.True(result, "Attempt to apply changes to workspace failed.")
                     Next
                 End Sub)
         End Function

src/VisualStudio/Core/Test/CodeModel/VisualBasic/CodeClassTests.vb

@@ -3154,7 +3154,20 @@ End Class
             Await TestElement(code,
                 Sub(state, codeClass)
                     For i = 1 To 100
-                        Dim variable = codeClass.AddVariable("x", "System.Int32")
+                        Dim initialDocument = state.FileCodeModelObject.GetDocument()
+                        Dim variable As EnvDTE.CodeVariable
+
+                        Try
+                            variable = codeClass.AddVariable("x", "System.Int32")
+                        Catch ex As InvalidOperationException
+                            Assert.False(True,
+$"Failed to add variable in loop iteration {i}!
+
+Document text:
+{initialDocument.GetTextAsync(CancellationToken.None).Result}")
+
+                            Throw ex
+                        End Try
 
                         ' Now, delete the variable that we just added.
                         Dim startPoint = variable.StartPoint
@@ -3165,7 +3178,7 @@ End Class
                         document = document.WithText(text)
 
                         Dim result = state.VisualStudioWorkspace.TryApplyChanges(document.Project.Solution)
-                        Assert.True(result)
+                        Assert.True(result, "Attempt to apply changes to workspace failed.")
                     Next
                 End Sub)
         End Function