Eh? You can’t prototype or explore if you have no idea what you are building. You obviously have some idea (3rd person shooter or accounting system?) but might

Eh? You can’t prototype or explore if you have no idea what you are building. You obviously have some idea (3rd person shooter or accounting system?) but might not be sure how to organize your code. However well written tests are independent of how you organize your code or any other implementation details. So tests are great even when you are just prototyping or exploring. You can rapidly change your code and have the tests ensure that it still works the same way. And the end result is a fully tested, easy to maintain code base. What’s not to love about that?