You could, but it’s tedious to write a new class for every scenario you want to test. Or to program for every scenario within that test implementation. And now

You could, but it’s tedious to write a new class for every scenario you want to test. Or to program for every scenario within that test implementation. And now you kind of should test your test implementation, and who wants to do that? Mocking makes it quick, easy, straightforward, and cuts out a ton of code noise from the test.