tests: Test our own custom QApplication

By default, `pytest-qt` initializes the default QApplication class that
PySide offers. Dangerzone, however, defines its own QApplication
subclass.

Create a `qapp_cls` fixture that will force `pytest-qt` to use this
subclass. For more info, see:
https://pytest-qt.readthedocs.io/en/latest/qapplication.html#testing-custom-qapplications

dangerzone/gui/__init__.py

@@ -37,8 +37,8 @@ class Application(QtWidgets.QApplication):
     document_selected = QtCore.Signal(list)
     application_activated = QtCore.Signal()
 
-    def __init__(self) -> None:
+    def __init__(self, *args: typing.Any, **kwargs: typing.Any) -> None:
-        super(Application, self).__init__()
+        super(Application, self).__init__(*args, **kwargs)
         self.setQuitOnLastWindowClosed(False)
         with open(get_resource_path("dangerzone.css"), "r") as f:
             style = f.read()

tests/conftest.py

@@ -0,0 +1,12 @@
+import typing
+
+import pytest
+
+from dangerzone.gui import Application
+
+
+# Use this fixture to make `pytest-qt` invoke our custom QApplication.
+# See https://pytest-qt.readthedocs.io/en/latest/qapplication.html#testing-custom-qapplications
+@pytest.fixture(scope="session")
+def qapp_cls() -> typing.Type[Application]:
+    return Application