Someone wants to test:

  function do_add(a, b, add) {
    return add(b, a);
  }

And does something like:

  do_add(1, 2, add)
  expect(add) to be called with (2, 1)

Then the function is changed to:

  function do_add(a, b, add) {
    return add(a, b);
  }

Oops, broke the test. Is this a type of behavior change that you expect would break the test? Often there are many ways to correctly do something and a good test should allow any of them.