I would consider it a replacement for throwaway tests. If I don't have a REPL, I often write a lot of little throwaway tests to deal with intermediate bits of

I would consider it a replacement for throwaway tests. If I don't have a REPL, I often write a lot of little throwaway tests to deal with intermediate bits of the code. They end up being redundant with the real tests. They're often really bad tests, in that they're tightly coupled to implementation details. I should delete them. And I often forget to. Which creates extra maintenance burden for myself and my teammates. If I do have a REPL, I do all of that extra intermediate verification junk in the REPL. It's often more effective, it's usually less effort, and it always reduces the volume of unnecessary brittle tests in the codebase.