| Since extending a class means including on the singleton class of the
class, this should now complain this:
``` ruby
module M
  extend Gitlab::Utils::Override
  override :f
  def f
    super.succ
  end
end
class C
  extend M
  def self.f
    0
  end
end
```
It should complain because `C.f` wasn't calling `M#f`.
This should pass verification:
``` ruby
module M
  extend Gitlab::Utils::Override
  override :f
  def f
    super.succ
  end
end
class B
  def self.f
    0
  end
end
class C < B
  extend M
end
```
Because `C.f` would now call `M#f`, and `M#f` does override something. | ||
|---|---|---|
| .. | ||
| merge_hash.rb | ||
| override.rb | ||
| strong_memoize.rb | ||