[PyQt] unit testing pyqt app components

[Florian Bruhin]

* oliver <oliver.schoenborn at gmail.com> [2015-08-31 23:38:31 -0400]:
> We have a large pyqt-based application, PyQt works awesome. We use python
> nose for unit tests of business logic, and we have a set of unit tests for
> the GUI components.

I'd recommend switching to pytest[1] with its excellent pytest-qt[2]
plugin which solves those problems for you ;)

It can even run nose tests, so you can gradually switch over.

It also has a way[3] to wait until a signal is emitted (with a
timeout) where it spins a QEventLoop.

(disclaimer: I'm a contributor to both pytest and the plugin)

[1] https://github.com/pytest-dev/pytest
[2] https://github.com/pytest-dev/pytest-qt
[3] https://pytest-qt.readthedocs.org/en/1.5.1/signals.html

> However, sometimes it appears that resources are not properly cleaned up
> between tests: a test will crash, or will not start unless we have put a
> "del some_qwidget_instance" in the teardown. Is it safe to re-use the same
> QApplication instance after its exec() has returned? I.e. can we do this:
> 
> app = QApplication([])
> my_gui_obj = MyGuiObj()  # derives from QWidget
> # other stuff
> app.exec()
> my_gui_obj2 = MyGuiObj()  # derives from QWidget
> # other stuff
> app.exec()
> my_gui_obj3 = MyGuiObj()  # derives from QWidget
> # other stuff
> app.exec()
> 
> Is there anything we should do to QApplication instance between tests
> (clear some caches, reset things like styles etc) so that each tests starts
> with a "fresh" QApplication? What is the recommended way to test multiple
> PyQt components independently of each other?

I don't think you should reuse a QApplication after you (I guess)
called QApplication::quit.

pytest-qt runs QApplication::processEvents before and after each test
- it's not ideal, but it's the best we could come up with so far.

Another solution might be to run a dedicated QEventLoop every time,
like the waitSignal thing in [3].

Florian

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