This is why/how they are a development tool. "Mocking interactions among objects", often breaking, taking too long to write (I expect to spend 30% dev on units

This is why/how they are a development tool. "Mocking interactions among objects", often breaking, taking too long to write (I expect to spend 30% dev on units, 30% on code rest thinking, planning, etc). Those are all indicators that your code/architecture is bad. Too complex, too coupled, too much concern, not layered into clean interfaces, etc.