I use the REPL as lightweight form of testing while I'm in the flow state, which is complementary to TDD. If there's too much code in the comment block, that's

I use the REPL as lightweight form of testing while I'm in the flow state, which is complementary to TDD. If there's too much code in the comment block, that's a good signal to move it into a formal test like you're saying, or at least move the code into a reusable function so the comment block can be shorter and focused on usage examples instead of implementation details.