It sounds like you write your tests based on the code you write rather than its expected behaviour. You can write a good set of tests when you know the initial

It sounds like you write your tests based on the code you write rather than its expected behaviour. You can write a good set of tests when you know the initial requirements, and not all requirements iterate at the same rate as the code. As you learn new requirements, you write new tests. The old ones don't go away (nor do the early requirements if they're good), even if you completely replace the implementing code.