Fix test_override_heading test

wagtail/admin/tests/test_edit_handlers.py

@@ -421,14 +421,15 @@ class TestFieldPanel(TestCase):
             field_panel.db_field
 
     def test_override_heading(self):
-        # unless heading is specified in keyword arguments, a bound edit handler should take its
+        # unless heading is specified in keyword arguments, an edit handler with bound form should take its
         # heading from the bound field label
-        self.assertEqual(self.end_date_panel.heading, self.end_date_panel.bound_field.label)
+        bound_panel = self.end_date_panel.bind_to(form=self.EventPageForm())
+        self.assertEqual(bound_panel.heading, bound_panel.bound_field.label)
 
         # if heading is explicitly provided to constructor, that heading should be taken in
         # preference to the field's label
         end_date_panel_with_overridden_heading = (FieldPanel('date_to', classname='full-width', heading="New heading")
-                                                  .bind_to(model=EventPage, request=self.request))
+                                                  .bind_to(model=EventPage, request=self.request, form=self.EventPageForm()))
         self.assertEqual(end_date_panel_with_overridden_heading.heading, "New heading")