mocking with jest-when

There is a handy library for mocking function return values, called jest-when:

when(fn)
  .calledWith(1)
  .mockReturnValue("yay!")
  .calledWith(2)
  .mockReturnValue("nay!")

Sidenote on mocks: After seeing Simple Made Easy talk by my engineering guru Rich Hickey, I realized that mocks most probably signal complecting of two unrelated components and thus point to accidental complexity. To remove the complexity, one can pass mocked data via function arguments instead.


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