from pyfakefs.fake_filesystem import FakeFileOpen def test_monkeypatch_with_fs(fs, monkeypatch): """Regression test for issue 1200""" fake_open = FakeFileOpen(fs) monkeypatch.setattr("builtins.open", fake_open, raising=False) def test_open(): """Tests if open is poisoned by the above test""" assert "built-in" in str(open)