The non-contextmanager form of pytest.raises was removed in pytest 5. http://doc.pytest.org/en/latest/deprecations.html#raises-warns-with-a-string-as-the-second-argument It was used here to support Python < 2.7, but that is no longer needed. https://github.com/psf/requests/pull/1503#issuecomment-22333666 Fixes https://github.com/psf/requests/issues/5304