You're right, there's no need to change the spy. Nevertheless, I believe that this way the asserts on the tests are clearer (and maybe faster because of having to do less indirections).

If we leave the code as it's now, then (e.g.)
assert.isTrue(createLockSpy.calledOnce); 
else it would read
assert.isTrue(navigator.mozSettings.createLock.calledOnce);
which I believe is less clear. If you still want me to change that I'll do it anyway.