[autotests] Add Q_CONSTRUCTOR_FUNCTION to X11 specific tests to force xcb

The X11 specific tests need to run on QT_QPA_PLATFORM xcb otherwise
they will crash. To enforce this without having to replace QTEST_MAIN
a Q_CONSTRUCTOR_FUNCTION is used to invoke a function which does nothing
except setting the env variable.

autotests/libxrenderutils/blendpicture_test.cpp

@@ -21,6 +21,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QLoggingCategory>
 #include <QX11Info>
 
+#include "../testutils.h"
 #include "../../libkwineffects/kwinxrenderutils.h"
 
 class BlendPictureTest : public QObject
@@ -55,5 +56,6 @@ void BlendPictureTest::testDontCrashOnTeardown()
     Q_UNUSED(picture2)
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(BlendPictureTest)
 #include "blendpicture_test.moc"

autotests/tabbox/test_tabbox_clientmodel.cpp

@@ -20,6 +20,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "test_tabbox_clientmodel.h"
 #include "mock_tabboxhandler.h"
 #include "clientmodel.h"
+#include "../testutils.h"
 
 #include <QtTest/QtTest>
 #include <QX11Info>
@@ -89,4 +90,5 @@ void TestTabBoxClientModel::testCreateClientListActiveClientNotInFocusChain()
     QCOMPARE(clientModel->rowCount(), 1);
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestTabBoxClientModel)

autotests/tabbox/test_tabbox_handler.cpp

@@ -19,6 +19,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 #include "mock_tabboxhandler.h"
 #include "clientmodel.h"
+#include "../testutils.h"
 #include <QtTest/QtTest>
 #include <QX11Info>
 
@@ -56,6 +57,7 @@ void TestTabBoxHandler::testDontCrashUpdateOutlineNullClient()
     tabboxhandler.show();
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestTabBoxHandler)
 
 #include "test_tabbox_handler.moc"

autotests/test_builtin_effectloader.cpp

@@ -21,6 +21,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "../effects/effect_builtins.h"
 #include "mock_effectshandler.h"
 #include "../scripting/scriptedeffect.h" // for mocking ScriptedEffect::create
+#include "testutils.h"
 // KDE
 #include <KConfig>
 #include <KConfigGroup>
@@ -563,5 +564,6 @@ void TestBuiltInEffectLoader::testLoadAllEffects()
     QCOMPARE(loadedEffects.at(1), QStringLiteral("mouseclick"));
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestBuiltInEffectLoader)
 #include "test_builtin_effectloader.moc"

autotests/test_client_machine.cpp

@@ -151,5 +151,6 @@ void TestClientMachine::emptyHostName()
     QCOMPARE(spy.isEmpty(), false);
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestClientMachine)
 #include "test_client_machine.moc"

autotests/test_screen_edges.cpp

@@ -30,6 +30,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "mock_client.h"
 #include "mock_screens.h"
 #include "mock_workspace.h"
+#include "testutils.h"
 // Frameworks
 #include <KConfigGroup>
 // Qt
@@ -861,5 +862,6 @@ void TestScreenEdges::testClientEdge()
     QCOMPARE(Cursor::pos(), QPoint(1, 50));
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestScreenEdges)
 #include "test_screen_edges.moc"

autotests/test_xcb_size_hints.cpp

@@ -371,5 +371,6 @@ void TestXcbSizeHints::geometryHintsBeforeRead()
     QCOMPARE(hints.windowGravity(), XCB_GRAVITY_NORTH_WEST);
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestXcbSizeHints)
 #include "test_xcb_size_hints.moc"

autotests/test_xcb_window.cpp

@@ -207,5 +207,6 @@ void TestXcbWindow::destroyNotManaged()
     QVERIFY(attribs);
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestXcbWindow)
 #include "test_xcb_window.moc"

autotests/test_xcb_wrapper.cpp

@@ -525,5 +525,6 @@ void TestXcbWrapper::testMotif()
     QTEST(hints.close(), "expectedClose");
 }
 
+Q_CONSTRUCTOR_FUNCTION(forceXcb)
 QTEST_MAIN(TestXcbWrapper)
 #include "test_xcb_wrapper.moc"

autotests/testutils.h

@@ -24,6 +24,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // XCB
 #include <xcb/xcb.h>
 
+namespace {
+    static void forceXcb() {
+        qputenv("QT_QPA_PLATFORM", QByteArrayLiteral("xcb"));
+    }
+}
+
 namespace KWin {
 
 /**