phivenv/Lib/site-packages/networkx/generators/tests/test_line.py

import pytest

import networkx as nx
from networkx.generators import line
from networkx.utils import edges_equal


class TestGeneratorLine:
    def test_star(self):
        G = nx.star_graph(5)
        L = nx.line_graph(G)
        assert nx.is_isomorphic(L, nx.complete_graph(5))

    def test_path(self):
        G = nx.path_graph(5)
        L = nx.line_graph(G)
        assert nx.is_isomorphic(L, nx.path_graph(4))

    def test_cycle(self):
        G = nx.cycle_graph(5)
        L = nx.line_graph(G)
        assert nx.is_isomorphic(L, G)

    def test_digraph1(self):
        G = nx.DiGraph([(0, 1), (0, 2), (0, 3)])
        L = nx.line_graph(G)
        # no edge graph, but with nodes
        assert L.adj == {(0, 1): {}, (0, 2): {}, (0, 3): {}}

    def test_multigraph1(self):
        G = nx.MultiGraph([(0, 1), (0, 1), (1, 0), (0, 2), (2, 0), (0, 3)])
        L = nx.line_graph(G)
        # no edge graph, but with nodes
        assert edges_equal(
            L.edges(),
            [
                ((0, 3, 0), (0, 1, 0)),
                ((0, 3, 0), (0, 2, 0)),
                ((0, 3, 0), (0, 2, 1)),
                ((0, 3, 0), (0, 1, 1)),
                ((0, 3, 0), (0, 1, 2)),
                ((0, 1, 0), (0, 1, 1)),
                ((0, 1, 0), (0, 2, 0)),
                ((0, 1, 0), (0, 1, 2)),
                ((0, 1, 0), (0, 2, 1)),
                ((0, 1, 1), (0, 1, 2)),
                ((0, 1, 1), (0, 2, 0)),
                ((0, 1, 1), (0, 2, 1)),
                ((0, 1, 2), (0, 2, 0)),
                ((0, 1, 2), (0, 2, 1)),
                ((0, 2, 0), (0, 2, 1)),
            ],
        )

    def test_multigraph2(self):
        G = nx.MultiGraph([(1, 2), (2, 1)])
        L = nx.line_graph(G)
        assert edges_equal(L.edges(), [((1, 2, 0), (1, 2, 1))])

    def test_multidigraph1(self):
        G = nx.MultiDiGraph([(1, 2), (2, 1)])
        L = nx.line_graph(G)
        assert edges_equal(L.edges(), [((1, 2, 0), (2, 1, 0)), ((2, 1, 0), (1, 2, 0))])

    def test_multidigraph2(self):
        G = nx.MultiDiGraph([(0, 1), (0, 1), (0, 1), (1, 2)])
        L = nx.line_graph(G)
        assert edges_equal(
            L.edges(),
            [((0, 1, 0), (1, 2, 0)), ((0, 1, 1), (1, 2, 0)), ((0, 1, 2), (1, 2, 0))],
        )

    def test_digraph2(self):
        G = nx.DiGraph([(0, 1), (1, 2), (2, 3)])
        L = nx.line_graph(G)
        assert edges_equal(L.edges(), [((0, 1), (1, 2)), ((1, 2), (2, 3))])

    def test_create1(self):
        G = nx.DiGraph([(0, 1), (1, 2), (2, 3)])
        L = nx.line_graph(G, create_using=nx.Graph())
        assert edges_equal(L.edges(), [((0, 1), (1, 2)), ((1, 2), (2, 3))])

    def test_create2(self):
        G = nx.Graph([(0, 1), (1, 2), (2, 3)])
        L = nx.line_graph(G, create_using=nx.DiGraph())
        assert edges_equal(L.edges(), [((0, 1), (1, 2)), ((1, 2), (2, 3))])


class TestGeneratorInverseLine:
    def test_example(self):
        G = nx.Graph()
        G_edges = [
            [1, 2],
            [1, 3],
            [1, 4],
            [1, 5],
            [2, 3],
            [2, 5],
            [2, 6],
            [2, 7],
            [3, 4],
            [3, 5],
            [6, 7],
            [6, 8],
            [7, 8],
        ]
        G.add_edges_from(G_edges)
        H = nx.inverse_line_graph(G)
        solution = nx.Graph()
        solution_edges = [
            ("a", "b"),
            ("a", "c"),
            ("a", "d"),
            ("a", "e"),
            ("c", "d"),
            ("e", "f"),
            ("e", "g"),
            ("f", "g"),
        ]
        solution.add_edges_from(solution_edges)
        assert nx.is_isomorphic(H, solution)

    def test_example_2(self):
        G = nx.Graph()
        G_edges = [[1, 2], [1, 3], [2, 3], [3, 4], [3, 5], [4, 5]]
        G.add_edges_from(G_edges)
        H = nx.inverse_line_graph(G)
        solution = nx.Graph()
        solution_edges = [("a", "c"), ("b", "c"), ("c", "d"), ("d", "e"), ("d", "f")]
        solution.add_edges_from(solution_edges)
        assert nx.is_isomorphic(H, solution)

    def test_pair(self):
        G = nx.path_graph(2)
        H = nx.inverse_line_graph(G)
        solution = nx.path_graph(3)
        assert nx.is_isomorphic(H, solution)

    def test_line(self):
        G = nx.path_graph(5)
        solution = nx.path_graph(6)
        H = nx.inverse_line_graph(G)
        assert nx.is_isomorphic(H, solution)

    def test_triangle_graph(self):
        G = nx.complete_graph(3)
        H = nx.inverse_line_graph(G)
        alternative_solution = nx.Graph()
        alternative_solution.add_edges_from([[0, 1], [0, 2], [0, 3]])
        # there are two alternative inverse line graphs for this case
        # so long as we get one of them the test should pass
        assert nx.is_isomorphic(H, G) or nx.is_isomorphic(H, alternative_solution)

    def test_cycle(self):
        G = nx.cycle_graph(5)
        H = nx.inverse_line_graph(G)
        assert nx.is_isomorphic(H, G)

    def test_empty(self):
        G = nx.Graph()
        H = nx.inverse_line_graph(G)
        assert nx.is_isomorphic(H, nx.complete_graph(1))

    def test_K1(self):
        G = nx.complete_graph(1)
        H = nx.inverse_line_graph(G)
        solution = nx.path_graph(2)
        assert nx.is_isomorphic(H, solution)

    def test_edgeless_graph(self):
        G = nx.empty_graph(5)
        with pytest.raises(nx.NetworkXError, match="edgeless graph"):
            nx.inverse_line_graph(G)

    def test_selfloops_error(self):
        G = nx.cycle_graph(4)
        G.add_edge(0, 0)
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)

    def test_non_line_graphs(self):
        # Tests several known non-line graphs for impossibility
        # Adapted from L.W.Beineke, "Characterizations of derived graphs"

        # claw graph
        claw = nx.star_graph(3)
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, claw)

        # wheel graph with 6 nodes
        wheel = nx.wheel_graph(6)
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, wheel)

        # K5 with one edge remove
        K5m = nx.complete_graph(5)
        K5m.remove_edge(0, 1)
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, K5m)

        # graph without any odd triangles (contains claw as induced subgraph)
        G = nx.compose(nx.path_graph(2), nx.complete_bipartite_graph(2, 3))
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)

        ## Variations on a diamond graph

        # Diamond + 2 edges (+ "roof")
        G = nx.diamond_graph()
        G.add_edges_from([(4, 0), (5, 3)])
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)
        G.add_edge(4, 5)
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)

        # Diamond + 2 connected edges
        G = nx.diamond_graph()
        G.add_edges_from([(4, 0), (4, 3)])
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)

        # Diamond + K3 + one edge (+ 2*K3)
        G = nx.diamond_graph()
        G.add_edges_from([(4, 0), (4, 1), (4, 2), (5, 3)])
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)
        G.add_edges_from([(5, 1), (5, 2)])
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)

        # 4 triangles
        G = nx.diamond_graph()
        G.add_edges_from([(4, 0), (4, 1), (5, 2), (5, 3)])
        pytest.raises(nx.NetworkXError, nx.inverse_line_graph, G)

    def test_wrong_graph_type(self):
        G = nx.DiGraph()
        G_edges = [[0, 1], [0, 2], [0, 3]]
        G.add_edges_from(G_edges)
        pytest.raises(nx.NetworkXNotImplemented, nx.inverse_line_graph, G)

        G = nx.MultiGraph()
        G_edges = [[0, 1], [0, 2], [0, 3]]
        G.add_edges_from(G_edges)
        pytest.raises(nx.NetworkXNotImplemented, nx.inverse_line_graph, G)

    def test_line_inverse_line_complete(self):
        G = nx.complete_graph(10)
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)

    def test_line_inverse_line_path(self):
        G = nx.path_graph(10)
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)

    def test_line_inverse_line_hypercube(self):
        G = nx.hypercube_graph(5)
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)

    def test_line_inverse_line_cycle(self):
        G = nx.cycle_graph(10)
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)

    def test_line_inverse_line_star(self):
        G = nx.star_graph(20)
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)

    def test_line_inverse_line_multipartite(self):
        G = nx.complete_multipartite_graph(3, 4, 5)
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)

    def test_line_inverse_line_dgm(self):
        G = nx.dorogovtsev_goltsev_mendes_graph(4)
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)

    def test_line_different_node_types(self):
        G = nx.path_graph([1, 2, 3, "a", "b", "c"])
        H = nx.line_graph(G)
        J = nx.inverse_line_graph(H)
        assert nx.is_isomorphic(G, J)


class TestGeneratorPrivateFunctions:
    def test_triangles_error(self):
        G = nx.diamond_graph()
        pytest.raises(nx.NetworkXError, line._triangles, G, (4, 0))
        pytest.raises(nx.NetworkXError, line._triangles, G, (0, 3))

    def test_odd_triangles_error(self):
        G = nx.diamond_graph()
        pytest.raises(nx.NetworkXError, line._odd_triangle, G, (0, 1, 4))
        pytest.raises(nx.NetworkXError, line._odd_triangle, G, (0, 1, 3))

    def test_select_starting_cell_error(self):
        G = nx.diamond_graph()
        pytest.raises(nx.NetworkXError, line._select_starting_cell, G, (4, 0))
        pytest.raises(nx.NetworkXError, line._select_starting_cell, G, (0, 3))

    def test_diamond_graph(self):
        G = nx.diamond_graph()
        for edge in G.edges:
            cell = line._select_starting_cell(G, starting_edge=edge)
            # Starting cell should always be one of the two triangles
            assert len(cell) == 3
            assert all(v in G[u] for u in cell for v in cell if u != v)