`ngMock` breaks during clean-up with mocked `$rootScope`

[gkalpak]

#13433 introduced $rootScope clean-up after each test. The implementation assumes that $rootScope will always have a $destroy() method, which might not be true for a mocked/decorated $rootScope, resulting in an error.

Also discussed in #13985 (comment).

[Narretz]

I think if you are mocking (essential) services then you need to provide their API surface. I would go as far as recommending against mocking things such as $injector, $rootScope etc.

[Narretz]

Ok, I see how this can be confusing if you inject this in a service but you don't actually use any of the functions of the rootScope. So I'm okay with fixing this.