Patch mostly looks good to me, but there should be a second test ensuring that the loader attribute gets *replaced*, even if it is already set to something else.

A similar test structure to the existing one should work, but replacing the "del types.__loader__" with:

    expected_loader_type = type(types.__loader__)
    types.__loader__ = "this will be replaced by the reload"

and then later:

    assertIs(type(types.__loader__), expected_loader_type)