Satin and Qt event loop

Qt comes with a really good testing library called QTest. It can be used to simulate keyboard and mouse input when testing the system. PyQt naturally includes the same library, but using it can be a bit tricky sometimes. Mouse input works quite fine, but keyboard input does not work well without event loop running in the background. It is possible to get around this, by instantiating QApplication and calling exec_ – method on it. At this point QApplication takes charge of things and execution leaves the test method.

There are several ways around this. One is to construct two threads, using one to send keyboard and mouse events to the system under test. One should note though, that the QApplication should be running in the main thread (it will helpfully notify you if this is not the case). Another thing is shared resources. Constructing QPixmap objects outside of the thread running QApplication is not advisable (you’ll be notified about this too).

Second option is to construct a QTimer, that will start execution of your test code. In this model you do not need to worry about multiple threads or shared resources.

Doing either one  can get tedious, especially if the amount of tests is more than two. Satin now has a class decorator satin_suite, that will take care of the basic steps, leaving the developer free to write more expressive tests. Essentially, the decorator will perform following steps:

  1. Replace setup-function with a version that creates instance of QApplication and calls the original setup-function.
  2. Replace teardown-function with a version that deallocates QApplication and calls the original teardown-function.
  3. Replace each test_* function with a version that will install a QTimer, start QApplication, execute test code and exit QApplication

Details are still rough and the system has some faults (like any exception or failure halting the execution of tests).

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