    def test_if_its_in_the_tree_anyhow_it_does_not_raise_an_error(self):
        """
        If a keyword refers to a path that isn't in the instance, the
        tree still properly returns a subtree for that path.
        """

        error = exceptions.ValidationError(
            "a message", validator="foo", instance={}, path=["foo"],
        )
        tree = exceptions.ErrorTree([error])
        self.assertIsInstance(tree["foo"], exceptions.ErrorTree)
If a keyword refers to a path that isn't in the instance, the
tree still properly returns a subtree for that path.
jsonschema/tests/test_exceptions.py