Some documentation about creating stubs is listed here: https://testbox.ortusbooks.com/mocking/mockbox/creating-mockbox It talks about making the stubs directory (generationPath) writable, and also the requirement that code in that directory must be cfinclude'able. That is a setup issue for our codebase, so we opted to go with the in-memory filesystem noted in the hint at the bottom of the page. As far as I can tell, MockBox does not work with ram:// paths. In MockGenerator there's an expandPath call (in the generate() method), and expandPath does not work with ram:// paths AFAIK. Furthermore, files cannot be cfinclude'd from ram:// paths without a mapping, so even without the expandPath the in-memory filesystem doesn't work.