QSignalSpy is not happy about KWin::Deleted*:
QWARN : SlidingPopupsTest::testWithOtherEffectWayland(wobblywindows, slide)
QSignalSpy: Unable to handle parameter 'deleted' of type 'KWin::Deleted*' of
method 'windowClosed', use qRegisterMetaType to register it.
Register KWin::Deleted* to fix the warning.