What I meant is that you will end up permanently with multiple solutions for the same problem if you try to change things gradually. This has several drawbacks:

What I meant is that you will end up permanently with multiple solutions for the same problem if you try to change things gradually. This has several drawbacks: Additional complexity having to support both versions, confusion with new developers about which variant to use, a higher likeliness that someone will add a third variant. You have to weigh the benefits of the new alternative against having a more complex code base/doing the grunt work of changing everything at once. So in this example you have to weigh the benefits of the two file tests against having tests that work uniformly.