[FIXED] Testing PySide Application using QProcess

Issue

I have a PySide application that spawns a worker application in a QProcess. The worker performs a simulation and creates result files to be read by the main application. I want to spawn the worker, give time for it to work, and then check the output. In my test function (I'm using py.test, if that helps), I cannot find a way to wait for the worker without blocking the main thread, thus not allowing the worker process to start and run.

def test_worker_thread():
    application = Application()  # Waits for and loads result files
    application.worker.start()  # Runs in a new process

    # How to wait right here without blocking thread?

    <wait_code>

    assert_correct_data(application.worker.results)

For the section called "wait_code", I have tried:

• Creating a local object with one attribute called done. I connect the worker.finished signal to setting done to True. I then used a time.sleep loop to block wait for the worker to be done.

  class WaitObject:
  
      def __init__(self):
          self.condition = False
  
      def set_true(self):
          self.condition = True
  
  wait = WaitObject()
  application.worker.finished(wait.set_true)
  
  while not wait.condition:
      time.sleep(1)
  

• I googled for methods to test asynchronous Qt code, and I came across QTest.qWait, which I could use in place of time.sleep() without blocking the event loop. However, qWait is not included in PySide.

• I have also tried creating a new event loop, like in this thread. However, this seems to block the event loop for application, so we cannot finish the worker.start function and load data while the worker is running.

  loop = QtCore.QEventLoop()
  application.worker.finished(loop.quit)
  loop.exec_()
  

Any tips?

Solution

It turns out option 3 actually works. My worker wasn't starting because of an unrelated error. Here is some skeleton code in its entirety:

def test_worker_thread():
    application = Application()  # Waits for and loads result files
    application.worker.start()  # Runs in a new process

    loop = QtGui.QEventLoop()
    application.worker.finished(loop.quit)  # Resume when worker done
    loop.exec_()  # Blocks at this line until loop quits

    assert_correct_data(application.worker.results)

I am going to work on an abstraction of this pattern. I am going to add a timeout using a singleshot QTimer that is connected to loop.quit, in case worker.finished is never called.

EDIT: Here is a blog post explaining in more detail.

Answered By - John David Reaver