Thanks for putting a name to this. Happens way too often when I start rewriting old code. I usually rename the test class of the old implementation to OldXTest

Thanks for putting a name to this. Happens way too often when I start rewriting old code. I usually rename the test class of the old implementation to OldXTest and try to keep the interface of the new code similar enough to enable a reasonably quick transition into the new code with proper unit testing.