How to properly start Qt with Qt Eventloop for GTest

JuliusCaesar

Hey,
I'd like to create some GTests on QT Objects. However, if need the Signals/Slots to work.
Therefore I run QApplication in main() and from main() I spawn a QThread() running Gtest.
I'm running Qt 5.12.8

/**
 * @brief Executes GTest. After Executing GTest it will stop the QApllication
*/
static void ExecuteGTest();

int main(int argc, char* argv[])
{


  ::testing::InitGoogleTest(&argc, argv);
  QApplication app(argc, argv);

  std::unique_ptr<QThread> pGTest(QThread::create(ExecuteGTest));
  pGTest->start();

  const int iGTestRes = app.exec();
  bool bIsRunning = pGTest->isRunning();
  if (bIsRunning)
  {
    //GTest thread is still running =>should not been happening....requesting exit
    //Request exit with error code
    pGTest->exit(-1);
    pGTest->wait();
  }
  return iGTestRes;
}

static void ExecuteGTest()
{
  {
    //perform checks to validate that Qt Eventloop is actually running
    const QThread* pCurrent = QThread::currentThread();
    ASSERT_TRUE(nullptr != pCurrent) << "This is no QThread";
    const auto* pEventLoop = pCurrent->eventDispatcher();
    ASSERT_TRUE(nullptr != pEventLoop) << "Eventloop is not running";
  }
  const int iRes = RUN_ALL_TESTS();
  //terminate the Qt Eventloop and return GTest Result
  QApplication::exit(iRes);
}

Now my Testcase is pretty simple

static bool mg_bTimerExpired = false;

static void OnTimerTick();

static void OnTimerTick()
{
  mg_bTimerExpired = false;
}



TEST(RunCameraUpdate, FirstTest)
{
  QTimer::singleShot(2000, nullptr, &OnTimerTick);
  
  std::this_thread::sleep_for(std::chrono::seconds(5));

  EXPECT_TRUE(mg_bTimerExpired);
}

Unfortunately OnTimerTick is never executed. Do you have an idea why?

thx for your help :)

Christian Ehrlicher

@JuliusCaesar said in How to properly start Qt with Qt Eventloop for GTest:

std::this_thread::sleep_for(std::chrono::seconds(5));

You block the event loop here so no signals can be send.

/edit: you're likely looking for QSignalSpy

JuliusCaesar

bit this code is run from a new spawned QThread.
Doesn't the Eventloop run in the main Thread()?

I tried

QThread* pCurrent = QThread::currentThread();
  pCurrent->sleep(5);

as well. This does not work either
Thx for the Tip with SignalSpy. I'll have a look at that :)

Christian Ehrlicher

@JuliusCaesar said in How to properly start Qt with Qt Eventloop for GTest:

Doesn't the Eventloop run in the main Thread()?

Every QThread has it's own eventloop when you don't overwrite run. See the documentation and objects create in a QThread have to use this eventloop. Otherwise a separate QThread would be useless.

JuliusCaesar

Hey,
thx for Your reply :)

When I manually call QCoreApplication::processEvents() after the wait time, all pending events are processed.
So this is a backup solution.

But I do not want to call processEvents in each testcase.

Is it possible to have 2 QThreads. One QThread with an working event which holds all QObjects and 1 where all Tests run in.
Or is there any other solution? Could you help finding my figuring this out?

How do non QT GUI applications process the event handling?

thx :)
greets

Christian Ehrlicher

@JuliusCaesar said in How to properly start Qt with Qt Eventloop for GTest:

How do non QT GUI applications process the event handling?

Exactly like the gui ones - the don't block the event loop and you should not do either. There is no reason for it.

JuliusCaesar

alright thx for your answer. I'll have to think about an alternate solution :)

Ccyros

Check my example here:
https://forum.qt.io/post/804638