Ah, fair enough! Though monkey patching is only possible in some dynamic languages, namely the ones where classes and modules are mutable hash tables. Note th

Ah, fair enough! Though monkey patching is only possible in some dynamic languages, namely the ones where classes and modules are mutable hash tables. Note that in ES6, unless you insert some special code via something like babel-rewire, imports can't be monkey patched. Also, Scheme is dynamically-typed and has no monkey patching. Anyway, I agree monkey patching in tests can be pretty convenient! But I personally think it's also a bad idea because it means that your tests are now coupled to the internal implementation of the code under test. That is, if you refactored the implementation, the test could break. Passing testable dependencies explicitly avoids this problem and avoids the need to monkey patch in tests.