'Restrict unit access to a certain group and confirm that a
warning is displayed.  Then, remove the access restriction
and verify that the warning no longer appears.'

def _set_restriction_on_unrestricted_unit(self, unit):

    self.assertFalse(unit.has_restricted_warning)
    unit.toggle_unit_access('Content    Groups', [self.content_group_a_id])
    self.assertTrue(unit.has_restricted_warning)
    unit.toggle_unit_access('Content    Groups', [self.content_group_a_id])
    self.assertFalse(unit.has_restricted_warning)
