See this comment: https://github.com/dotnet/roslyn/blob/a4eb40996b456c30977e6b7291e7e1fc52a750b6/src/Workspaces/CoreTestUtilities/ExportProviderCache.cs#L206-L212
See this comment:
roslyn/src/Workspaces/CoreTestUtilities/ExportProviderCache.cs
Lines 206 to 212 in a4eb409