def METHOD_NAME(self) -> None:
    """Test adding an edge."""
    source = _get_random_node()
    target = _get_random_node()
    graph = Graph()
    graph.add_node(source)
    graph.add_node(target)
    result = graph.add_edge(source_id=source.id, target_id=target.id)
    self.assertEqual(True, result)
    edges = graph.edges
    self.assertEqual(1, len(edges))
    edge = edges[0]
    self.assertEqual(source, edge._source)
    self.assertEqual(target, edge._target)