Tests can waste time because developers treat the test suite as its own application that needs to be managed.

Stop. Doing. This.

With some exceptions, tests should NOT be DRY. They should be dumb, explicit, repetitive, conventional, and as independent as possible. This allows tests to be more quickly understood by any given developer and changed without breaking other tests for stupid reasons unrelated to the actual application.

So much of my time has been wasted at every job I've had because developers believed that the tests should be really clever and use a bunch of magic and shared logic to "save time", which in reality becomes difficult to manage and understand. Most tests are crap for that reason alone.