I just reviewed a pull request with a test case like (pseudo code):

# Test MyService

const mock = createMock(myService.myMethod)
.whenCalledWith("foo")
.returns("bar");
assert(mock.myMethod("foo") === "bar"));

Why though? Why are we testing the mock? What is happening here? This test has no reason of being there instead of a fuzzy feeling that we now have unit test to lure us into a false sense of security.

I asked why we don't do an integration test. Response was: "They are slow."

Well, duh, but at least they would actually test something.

What do you gain by asserting that the mock is working the way you set it up?