 <blockquote> <p>should I create an unit test for a string formatting that's supossed to be user-input? Or is it just wasting my time while I just can check it in the actual code?</p> </blockquote> <p>Not sure I understand what you mean, but the tests you write in TDD are supposed to test your production code. They aren't tests that check user input.</p> <p>To put it another way, there can be TDD unit tests that test the user input validation <em>code</em>, but there can't be TDD unit tests that validate the user input itself.</p>