> Making sure tests pass can be challenging to handle with the unknowns of implementation detail. After all, if you expect parseInt to act one way and it behave

> Making sure tests pass can be challenging to handle with the unknowns of implementation detail. After all, if you expect parseInt to act one way and it behaves another, you will likely have to rewrite all tests that worked off that assumption. Isn't this kind of the point of TDD? TDD makes it harder to write tests based on assumptions about implementation details, making it less likely that you'll make such assumptions. You end up with less unnecessary coupling between your tests and the implementation details of the code they test, which means fewer false failures (tests that fail because the structure changes, rather than the behavior), and a more robust test suite.