Testing QApplication

If your tests need access to a full QApplication instance to e.g. test exit behavior or custom application classes, you can use the techniques described below:

Testing QApplication.exit()

Some pytest-qt features, most notably waitSignal and waitSignals, depend on the Qt event loop being active. Calling QApplication.exit() from a test will cause the main event loop and auxiliary event loops to exit and all subsequent event loops to fail to start. This is a problem if some of your tests call an application functionality that calls QApplication.exit().

One solution is to monkeypatch QApplication.exit() in such tests to ensure it was called by the application code but without effectively calling it.

For example:

def test_exit_button(qtbot, monkeypatch):
    exit_calls = []
    monkeypatch.setattr(QApplication, "exit", lambda: exit_calls.append(1))
    button = get_app_exit_button()
    qtbot.click(button)
    assert exit_calls == [1]

Or using the mock package:

def test_exit_button(qtbot):
    with mock.patch.object(QApplication, "exit"):
        button = get_app_exit_button()
        qtbot.click(button)
        assert QApplication.exit.call_count == 1

Testing Custom QApplications

It’s possible to test custom QApplication classes, but you need to be careful to avoid multiple app instances in the same test. Assuming one defines a custom application like below:

from PyQt5.QtWidgets import QApplication


class CustomQApplication(QApplication):
    def __init__(self, *argv):
        super().__init__(*argv)
        self.custom_attr = "xxx"

    def custom_function(self):
        pass

If your tests require access to app-level functions, like CustomQApplication.custom_function(), you can override the built-in qapp fixture in your conftest.py to use your own app:

@pytest.fixture(scope="session")
def qapp():
    yield CustomQApplication([])

Setting a QApplication name

By default, pytest-qt sets the QApplication.applicationName() to pytest-qt-qapp. To use a custom name, you can set the qt_qapp_name option in pytest.ini:

[pytest]
qt_qapp_name = frobnicate-tests