SinonJS

Hello,

Instead of `mock = makeMockFn();` you may want to require [sinon](http://sinonjs.org/docs/#stubs) and call `mock = sinon.stub()` you'll then be able to leverage the power of Sinon API.

My two cents :)

Start by locating makeMockFn and its callers in the repository, then inspect how the project currently creates and verifies spies. Review the Sinon suggestion alongside the existing dependency setup and tests; done means the relevant mock behavior is preserved and the test suite passes.

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