QTestLib: flush DeferredDelete events between every test

This makes qtestlib behave more like real Qt applications with an
event loop, where exiting the application does indeed flush deleteLaters.
And since every test method is supposed to be independent from other
test methods, we should even cleanup between tests.

For "app less" tests, no flushing happens.

Real life use cases:

* A unittest for some code (e.g. KIO job) which uses a socket, runs an
event loop until the socket communication is done, and ends. However
slotDisconnected() does, as recommended, socket->deleteLater(). So the
test finishes before the socket has a chance to actually get deleted,
and memory leak tools flag a memory leak, which doesn't actually happen
outside the unittest.

* Deleting a QWebEngineView with deleteLater is even worse than a memleak,
it leads to an assert (from a global object destructor) in QtWebEngine
if the view deletion hasn't actually been processed.

Change-Id: I18fc822fd26988a0fa4e75313c1947fcaa7d9e56
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/testlib/qtestcase.cpp b/src/testlib/qtestcase.cpp
index eeaa30e9a0..8f8bb83f11 100644
--- a/src/testlib/qtestcase.cpp
+++ b/src/testlib/qtestcase.cpp
@@ -901,6 +901,10 @@ void TestMethods::invokeTestOnData(int index) const
             if (m_cleanupMethod.isValid())
                 m_cleanupMethod.invoke(QTest::currentTestObject, Qt::DirectConnection);
 
+            // Process any deleteLater(), like event-loop based apps would do. Fixes memleak reports.
+            if (QCoreApplication::instance())
+                QCoreApplication::sendPostedEvents(nullptr, QEvent::DeferredDelete);
+
             // If the test isn't a benchmark, finalize the result after cleanup() has finished.
             if (!isBenchmark)
                 QTestResult::finishedCurrentTestDataCleanup();