def test_contract(self) -> None:
g = MultiGraph([(1, 2), (1, 3), (2, 3), (2, 4), (2, 2), (2, 2)])
assert g[1].adj_vertices() == {
g[2],
g[3],
}, "vertex 1 should be adjacent to vertices 2 and 3"
assert (
g.get_edge(1, 3).multiplicity == 1
), "before edge contraction, edge (1, 3) should have multiplicity 1"
assert g.get_edge(
2, 2).multiplicity == 2, "vertex 2 should have two loops"
g.get_edge(1, 2).contract(remove_loops=False)
assert g[1].adj_vertices() == {
g[1],
g[3],
g[4],
}, "after edge contraction, vertex 1 should be adjacent to vertices 1, 3, and 4"
assert (
g.get_edge(1, 3).multiplicity == 2
), "after edge contraction, edge (1, 3) should have multiplicity 2"
assert g[1].loop_edge, "vertex 1 should have loop edge (1, 1)"
print(f"\nDEBUG: g[1].loop_edge => {g[1].loop_edge}\n")
assert g[
1].loop_edge.multiplicity == 3, "loop edge should have multiplicity 3"
assert not g.has_vertex(
2), "after edge contraction, vertex 2 should be removed"
g2 = MultiDiGraph([(1, 2), (2, 4), (2, 2), (2, 2)])
g2.get_edge(1, 2).contract(remove_loops=True)
assert not g2[
1].loop_edge, "loop edge should be removed after edge contraction"
def test_remove(self) -> None:
g = MultiGraph([(1, 2), (1, 2), (2, 3)])
assert g.has_edge(1,
2), "prior to removal, graph should have edge (1, 2)"
assert not g[1].is_isolated(
), "vertex 1 should not be isolated prior to edge removal"
g.get_edge(1, 2).remove(remove_semi_isolated_vertices=False)
assert not g.has_edge(
1, 2), "after removal, graph should not have edge (1, 2)"
assert g.has_vertex(
1
), "after edge removal, isolated vertex 1 should still be in graph"
assert g[1].is_isolated(
), "vertex 1 should be isolated after edge removal"
g2 = MultiGraph([(1, 2), (1, 2), (1, 1), (1, 1), (2, 3)])
g2.get_edge(1, 2).remove(remove_semi_isolated_vertices=True)
assert not g2.has_vertex(
1
), "after edge removal, semi-isolated vertex 1 should have been removed"