🔗 Checking Efx - testable effects for Elixir

Mocking in Elixir is always a hot topic, mainly because of people coming from different other technologies having different expectation. The most "cannonical" solution, Mox, gives a lot of security with regard to what the fake implementation returns, but requires a bit of a ceremony from the programmer. Other solutions like Mock, Rewire or Bypass offer more ad-hoc mocking, but t the price of the tests heving to be synchronous. Then there's Mimic, which offers ad-hoc mocking and supports async tests.

In this busy area, a new library appeared very recently. It's called Efx and its description does not even mention mocking:

A library to declaratively write testable effects It immediately cought m attention, because it seems to implement what I described as “purity injection” some time ago. As a programmer, you write a default impure implementation of the code, but you mark it as an “effect”. Then in tests you replace a stateful implementation with something more predictable (you “inject purity”) and you can enjoy nice, stable and fast tests.

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