Comment by dpark

> you change the internal behaviors of a function/method and now the mocks interact differently with the underlying code, forcing you to change the mocks

Rarely should a mock be “interacting with the underlying code”, because it should be a dead end that returns canned data and makes no other calls.

If your mock is calling back into other code you’ve probably not got a mock but some other kind of “test double”. Maybe a “fake” in Martin Fowler’s terminology.

If you have test doubles that are involved in a bunch of calls back and forth between different pieces of code then there’s a good chance you have poorly factored code and your doubles are complex because of that.

Now, I won’t pretend changes don’t regularly break test doubles, but for mocks it’s usually method changes or additions and the fix is mechanical (though annoying). If your mocks are duplicating a bunch of logic, though, then something else is going on.