Agile -> YAGNI -> TDD Agile warns against building stuff you don't need. TDD means that test provide the justification for feature work. If your feature work

Agile -> YAGNI -> TDD Agile warns against building stuff you don't need. TDD means that test provide the justification for feature work. If your feature work isn't making a failing test past, you don't need that feature work. Obviously this assumes that your tests are justified (ideally there is a stack of tests leading all the way to the end user experiment), but that's much easier to get right than justifying untested feature work.