Another aspect related to this point is that we have a slow backend system and we wanted our JavaScript tests to be blazingly fast, also the integration tests.

Another aspect related to this point is that we have a slow backend system and we wanted our JavaScript tests to be blazingly fast, also the integration tests. I hate waiting for tests. Now I can run ours all the time because they don't use any time at all (well, okey, they take a second ...).