Remember that IIFE's are basically equivalent to variable definition and assignment. The only reason we even have to go through the trouble of using them is due to JS not having block scope.
Yeah, I'm aware I can do that, but it gets a bit painful for code that is stateful & executes on load (like IIFE does). You end up having to write a separate test script to run in a separate process for each test case...way slower than if you can isolate the module and 'restart' it in a closure for each test.
A different approach that might work for me would be to subvert require.js, so that it pulls in mocks. I see there's other people thinking along the same lines:
https://github.com/tigbro/requirejs-factory-plugin
