Comment by lmm

> testing exactly the same behaviour in several places

I think that's actually fine. Particularly if you're doing a testing pyramid style approach where you do a lot of tests of some piece of low level logic and then a few tests of the higher level piece that makes use of that lower level logic, I don't see any problem with the higher level test covering a codepath that's also used in the lower level test. If anything I find it makes it easier to understand and debug failures - you know that the behaviour of the lower level piece hasn't changed because otherwise the lower level test would have failed, so the bug can only be in the higher level component itself.