human
Solve the following python programming problem given the following code:
@pytest.fixture()
def mock_fetch(mock_archive):
assistant
#Here is the Python code you requested.

    """Fake the URL for a package so it downloads from a file.
    """
    fetcher = FetchStrategyComposite()
    fetcher.append(URLFetchStrategy(mock_archive.url))
    @property
    def fake_fn(self):
        return fetcher
    orig_fn = PackageBase.fetcher
    PackageBase.fetcher = fake_fn
    (yield)
    PackageBase.fetcher = orig_fn