Garbage collect after each test requiring a qapp

Attempts to fix a random test failure with the jupyter console on
macOS by ensuring that widgets are garbage collected promptly.
Refs #22063

qt/python/mantidqt/utils/qt/testing/__init__.py

@@ -20,6 +20,7 @@
 from __future__ import absolute_import
 
 from inspect import isfunction, ismethod
+import gc
 
 from qtpy.QtCore import Qt
 from qtpy.QtWidgets import QApplication
@@ -74,6 +75,7 @@ def _requires_qapp_impl(test_method):
             QAPP = QApplication([''])
         test_method(self)
         QAPP.closeAllWindows()
+        gc.collect()
 
     return _wrapper
 

qt/python/mantidqt/widgets/test/test_jupyterconsole.py

@@ -34,16 +34,18 @@ class InProcessJupyterConsoleTest(unittest.TestCase):
         self.assertTrue(hasattr(widget, "kernel_manager"))
         self.assertTrue(hasattr(widget, "kernel_client"))
         self.assertTrue(len(widget.banner) > 0)
+        del widget
 
     def test_construction_with_banner_replaces_default(self):
         widget = InProcessJupyterConsole(banner="Hello!")
         self.assertEquals("Hello!", widget.banner)
+        del widget
 
     def test_construction_with_startup_code_adds_to_banner_and_executes(self):
         widget = InProcessJupyterConsole(startup_code="x = 1")
         self.assertTrue("x = 1" in widget.banner)
         self.assertEquals(1, widget.kernel_manager.kernel.shell.user_ns['x'])
-
+        del widget
 
 if __name__ == '__main__':
     unittest.main()