Did you ever think that most of your test functions were actually the same test code, but with different data inputs and expected results/exceptions ? pytest-cases leverages pytest and its great @pytest.mark.parametrize decorator, so that you can separate your test cases from your test functions. In addition, pytest-cases provides several useful goodies to empower pytest. In particular it improves the fixture mechanism to support "fixture unions". This is a major change in the internal pytest engine, unlocking many possibilities such as using fixture references as parameter values in a test function.