pytest-twisted is a plugin for pytest, which allows to test code, which uses the twisted framework. test functions can return Deferred objects and pytest will wait for their completion with this plugin.

Install the plugin with:

pip install pytest-twisted

The plugin must be enabled. This can be done in the following ways:

1. Run py.test with the --twisted command line option

2. Put the following into conftest.py:

   pytest_plugins = "pytest_twisted"
   

3. Put the following into pytest.ini:

   [pytest]
   twisted = 1
   

Using twisted.internet.defer.inlineCallbacks as a decorator for test functions, which take funcargs, does not work. Please use pytest.inlineCallbacks instead:

@pytest.inlineCallbacks
def test_some_stuff(tmpdir):
    res = yield threads.deferToThread(os.listdir, tmpdir.strpath)
    assert res == []

pytest.blockon allows fixtures to wait for deferreds:

@pytest.fixture
def val():
    d = defer.Deferred()
    reactor.callLater(1.0, d.callback, 10)
    return pytest.blockon(d)

Some libraries (e.g. corotwine) need to know the greenlet, which is running the twisted reactor. It's available from the twisted_greenlet funcarg. The following code can be used to make corotwine work with pytest-twisted:

@pytest.fixture(scope="session", autouse=True)
def set_MAIN(request, twisted_greenlet):
    from corotwine import protocol
    protocol.MAIN = twisted_greenlet

That's all.