[PyQt] Unit testing PyQt applications

Mads Ipsen madsipsen at gmail.com
Wed Mar 14 14:22:34 GMT 2012

Sorry for a late reply - but thanks for a very useful answer. Got one 
more question though.

How would you technically moc QFileDialog.exec_ to avoid that the unit 
test is halted by the Dialog popping up in its own event loop. Anyway, 
this is how I do it:

class Proxy:
     def __init__(self):
         self._called = False

     def caller(self, *args):
         self._called = args

     def called(self):
         return self._called

proxy = Proxy()
new_exec = proxy.exec_
old_exec = QtGui.QFileDialog.exec_
QtGui.QFileDialog.exec_ = new_exec

   ... Then do testing and query proxy.called() to test that the 
QFileDialog was called

Finally clean up and reinsert the old exec_ method.

QtGui.QFileDialog.exec_ = new.instancemethod(old_exec, None, 

Makes sense?

On 07/03/2012 18:13, Andreas Pakulat wrote:
> On 07.03.12 15:42:34, Mads Ipsen wrote:
>> OK, I agree, the snippets I provided were not nice, and I apologize
>> for that.
>> But suppose that the constructor in your class starts a thread that
>> generates say an icon for a QStandardItem. Then you want to make
>> sure that the thread has finished before you test that the icon has
>> been created.
>> * What would be the proper way of unit testing this?
> I'd try to put in some moc-objects and split the testing. So one
> unit-test would just test the loading of the icon from whatever source
> it comes, without a thread in a blocking way.
> Another unit-test would put in a moc-object that immediately returns the
> icon so you can be sure that the amount of time the thread needs to run
> is relatively small. Then in the unit-test, create the widget and then
> let the main thread sleep for a bit so the background thread finishes.
> Afterwards verify the moc-icon is properly retrieved. You don't need an
> event loop here yet, unless you want the widget to be actually drawn.
>> * How should starting/stopping the event loop be handled?
> Hmm, the Qt unit-test framework works by starting the event-loop and
> triggering the unit-test functions via a timer. I guess this could also
> be done in python with the unittest framework somehow.
> Personally I'd probably avoid testing the actual event-loop-requiring
> bits of the application via unit-tests completely. Instead I'd go for a
> gui-test-tool to test those parts and use unit-tests for all the
> business-logic and non-gui stuff.
> Andreas
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| Mads Ipsen                                          |
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