Autotests with this code pattern can be flaky on XCB:

QWindow window;
window.show();
window.requestActivate();
QVERIFY(QTest::qWaitForWindowActive(&window));

show() causes the window to get activated. On QXcbWindow level, the activation may get deferred if QXcbWindow::requestActivateWindow() is reached when the window hasn't been mapped (=sown) yet. The explicit call to requestActivate() may also cause a deferred activation. When both activations find that another one is ongoing, both return with a no-op.