Replace the original function with a wrapper that calls the function then does the side effect. This could effectively be something like a decorator. As far a

Replace the original function with a wrapper that calls the function then does the side effect. This could effectively be something like a decorator. As far as mocking time objects, look into pytest.freezegun. You should be able to control the date and time as you move forward. I was able to mock out the datetime.now() at some point in the past. It wasn't with freezegun...