add timeout before adding signalfile to prevent graphic view segfaults

tests/QtTestCase.py

@@ -31,6 +31,8 @@ class QtTestCase(unittest.TestCase):
         self.form = MainController()
 
     def add_signal_to_form(self, filename: str):
+        QApplication.instance().processEvents()
+        QTest.qWait(1)
         self.form.add_signalfile(get_path_for_data_file(filename))
 
     def tearDown(self):