def test_change_public_access_file(self):
        """Test the basics of changing public access to a file."""
        a_file = self.vgw.make_file(self.root.id, 'a-file.txt')
        # It has no public ID
        self.assertIsNone(a_file.public_uuid)
        # It now has a public ID
        self.assertIsNotNone(
            self.vgw.change_public_access(a_file.id, True).public_uuid)
        # Disabled it, back to None
        self.assertIsNone(
            self.vgw.change_public_access(a_file.id, False).public_uuid)