> I especially dont see what is gained by writing the test after.
I assume you mean versus writing it first, rather than versus not writing it at all.
I've found that TDD works well for bottom-up coding, but not so well for top-down.
With bottom up, I can write the test for a piece at the bottom, write the code to pass the test, and move on. With top-down, if I write the test first, it might be a long while before I have that top-level working, because the bottom bits don't exist yet.
When I feel it's better to write things top-down, I'll often use TDD for the bottom bits I need to write, but for the bits above that, I'll write the tests "on my way back up".
I assume you mean versus writing it first, rather than versus not writing it at all.
I've found that TDD works well for bottom-up coding, but not so well for top-down.
With bottom up, I can write the test for a piece at the bottom, write the code to pass the test, and move on. With top-down, if I write the test first, it might be a long while before I have that top-level working, because the bottom bits don't exist yet.
When I feel it's better to write things top-down, I'll often use TDD for the bottom bits I need to write, but for the bits above that, I'll write the tests "on my way back up".