`UnitTest::cleanup()` shall drain any remaining signals or events.

Any signals or events which do significant work (including deleting objects marked with `deleteLater()`) may cause segmentation faults or use-after-free errors.

src/qgcunittest/UnitTest.cc

@@ -134,6 +134,12 @@ void UnitTest::cleanup(void)
         QEXPECT_FAIL("", "Expecting failure due internal testing", Continue);
     }
     QCOMPARE(_missedFileDialogCount, 0);
+
+    // Don't let any lingering signals or events cross to the next unit test.
+    // If you have a failure whose stack trace points to this then
+    // your test is leaking signals or events. It could cause use-after-free or
+    // segmentation faults from wild pointers.
+    qgcApp()->processEvents();
 }
 
 void UnitTest::setExpectedMessageBox(QMessageBox::StandardButton response)