def METHOD_NAME(self) -> None:
    """Test a partial mapping on a small graph."""
    graph = rx.generators.path_graph(4)
    mapping = {0: 3}
    swapper = ApproximateTokenSwapper(graph)  # type: ApproximateTokenSwapper[int]
    out = list(swapper.map(mapping))
    self.assertEqual(3, len(out))
    util.swap_permutation([out], mapping, allow_missing_keys=True)
    self.assertEqual({3: 3}, mapping)