tern then the package will be checked for a 'load_tests' function. If
        this exists then it will be called with (loader, tests, pattern) unless
        the package has already had load_tests called from the same discovery
        invocation, in which case the package module object is not scanned for
        tests - this ensures that when a package uses discover to further
        discover child tests that infinite recursion does not happen.

        If load_tests exists then discovery does *not* recurse into the package,
        load_tests is responsible for loading all tests in the package.

        The pattern is deliberately not stored as a loader attribute so that
        packages can continue discovery themselves. top_level_dir is stored so
        load_tests does not need to pass this argument in to loader.discover().

        Paths are sorted before being imported to ensure reproducible execution
        order even on filesystems with non-alphabetical ordering like ext3/4.
        FNTr