CppEditor/CppTools: Avoid triggering garbage collector on editor close in tests

Closing an editor might trigger a timer which leads to the invocation of
the garbage collector. This is unfavourable for the plugin tests since a
test function closing an editor might influence a subsequent test
function (e.g. files get removed from the global snapshot although they
were added shortly before).

Change-Id: Ia80c11f99e2437fe145dc2d983b21962539b5181
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cppmodelmanager_test.cpp

@@ -771,8 +771,9 @@ struct EditorCloser {
     EditorCloser(Core::IEditor *editor): editor(editor) {}
     ~EditorCloser()
     {
+        using namespace CppTools;
         if (editor)
-            Core::EditorManager::closeEditor(editor);
+            QVERIFY(Tests::TestCase::closeEditorWithoutGarbageCollectorInvocation(editor));
     }
 };