Updating tests using Moq to workaround Roslyn changes

https://roslyn.codeplex.com/workitem/246 affects usage of code with the
latest build of Roslyn with Moq v4.2. The workaround involves ensuring a
closure is created. Updating affected tests to make ToString() calls on
local variables to create these closures.
I'll go ahead and check this in to unblock the CI. We'll revert these changes once we get a new build of Moq (which is the current plan).