Pass program name to QApplication contructor (#515)

QCommandLineParser needs QApplication to be initialized with at list one
argument: The name of the program.

Closes #483

.pre-commit-config.yaml

@@ -43,6 +43,6 @@ repos:
     -   id: rst
         name: rst
         entry: rst-lint --encoding utf-8
-        files: ^(CHANGELOG.rst|HOWTORELEASE.rst|README.rst)$
+        files: ^(HOWTORELEASE.rst|README.rst)$
         language: python
         additional_dependencies: [pygments, restructuredtext_lint]

CHANGELOG.rst

@@ -1,3 +1,20 @@
+UNRELEASED
+-----------
+
+- ``qapp`` now sets up the ``QApplication`` instance with a command line argument like this
+  ``QApplication([prog_name])`` instead of using an empty list ``QApplication([])``.
+  Here ``prog_name`` is the name of the app which defaults to ``pytest-qt-app``, but can
+  be redefined in the ``pytest.ini`` file, see :ref:`qapp fixture<setting-qapp-name>`.
+  Alternatively, the arguments that will be passed to ``QApplication`` can be defined
+  explicitly using the ``qapp_args`` fixture. This means that the default behavior of
+  the ``qapp_args`` fixture is now also changed accordingly: it now returns the list
+  ``[prog_name]`` instead of an empty list. Thanks to `@The-Compiler`_ (`#483`_) and
+  `@hakonhagland`_ (`#515`_).
+
+..  _#515: https://github.com/pytest-dev/pytest-qt/pull/515
+..  _#483: https://github.com/pytest-dev/pytest-qt/issues/483
+
+
 4.2.0 (2022-10-25)
 ------------------
 
@@ -731,6 +748,7 @@ First working version.
 .. _@fabioz: https://github.com/fabioz
 .. _@fogo: https://github.com/fogo
 .. _@gqmelo: https://github.com/gqmelo
+.. _@hakonhagland: https://github.com/hakonhagland
 .. _@itghisi: https://github.com/itghisi
 .. _@jdreaver: https://github.com/jdreaver
 .. _@mitya57: https://github.com/mitya57

docs/qapplication.rst

@@ -75,6 +75,8 @@ If your tests require access to app-level functions, like
 The ``qapp`` fixture will then use the returned class instead of the default
 ``QApplication`` from ``QtWidgets``.
 
+.. _setting-qapp-name:
+
 Setting a QApplication name
 ---------------------------
 

src/pytestqt/plugin.py

@@ -12,7 +12,7 @@
 
 
 @pytest.fixture(scope="session")
-def qapp_args():
+def qapp_args(pytestconfig):
     """
     Fixture that provides QApplication arguments to use.
 
@@ -23,9 +23,19 @@ def qapp_args():
 
        @pytest.fixture(scope="session")
        def qapp_args():
-           return ["--arg"]
+           return ["prog_name", "--arg=foo"]
+
+
+    Note that it can only be overridden once at session scope.
+    It is not possible to override this per unit test since a QApplication
+    cannot be destroyed and recreated within the same app.
+
+    The default value is a list with one element which is determined the same
+    way as for ``QApplication.applicationName()``,
+    see :ref:`qapp fixture<setting-qapp-name>` for more information.
+
     """
-    return []
+    return [pytestconfig.getini("qt_qapp_name")]
 
 
 @pytest.fixture(scope="session")

tests/test_basics.py

@@ -546,7 +546,7 @@ def test_qapp_args(testdir):
 
         @pytest.fixture(scope='session')
         def qapp_args():
-            return ['--test-arg']
+            return ['prog_name', '--test-arg']
         """
     )
     testdir.makepyfile(
@@ -559,6 +559,22 @@ def test_args(qapp):
     result.stdout.fnmatch_lines(["*= 1 passed in *"])
 
 
+def test_qapp_args_default(testdir):
+    """
+    Test QApplication default arguments.
+    """
+
+    testdir.makepyfile(
+        """
+        def test_args(qapp):
+            args = qapp.arguments()
+            assert args[0] == 'pytest-qt-qapp'
+    """
+    )
+    result = testdir.runpytest_subprocess()
+    result.stdout.fnmatch_lines(["*= 1 passed in *"])
+
+
 def test_importerror(monkeypatch):
     def _fake_import(name, *args):
         raise ModuleNotFoundError(f"Failed to import {name}")

tests/test_wait_signal.py

@@ -617,7 +617,7 @@ class TestCallback:
     @staticmethod
     def get_signal_from_code(signaller, code):
         """Converts a code such as 'A1' to a signal (signaller.signal_args for example)."""
-        assert type(code) == str and len(code) == 2
+        assert type(code) is str and len(code) == 2
         signal = signaller.signal_args if code[0] == "A" else signaller.signal_args_2
         return signal