My experience is that it's painful if you don't have any idea of what you're doing; it's not the testing itself per se but rather the fact that if you're iterat

My experience is that it's painful if you don't have any idea of what you're doing; it's not the testing itself per se but rather the fact that if you're iterating rapidly on the code your tests will need to be rewritten over and over again. Large libraries of unit tests are invaluable for catching regressions, but they tend to impose a certain amount of friction on code changes and refactorings. So personally, I tend to do TDD when I know where I'm going, but for exploratory programming I write the minimal amount of high-level tests to test things end-to-end and make sure things kind of work at all and back-fill more detailed tests once the code has settled down a bit.