In my experienced years of development: - with TDD - implementation first and then tests - just implementation without test, I recently came to the following

In my experienced years of development: - with TDD - implementation first and then tests - just implementation without test, I recently came to the following conclusion: If you perform TDD, your specification that you try to implement are the business requirements / the goals you like to achieve. If you don't perform TDD, your specification becomes the algorithm/thing itself you are developing and a (potentially fuzzy) idea in your head.