def test_has_marked_path():
graph = MarkedPatternGraph(nodes=['a', 'b'])
graph.add_undirected_edge(('a', 'b'))
graph.add_marked_arrowhead(('a', 'b'))
assert graph.has_marked_arrowhead(('a', 'b')) == True
graph.add_undirected_edge(('b', 'c'))
assert graph.has_marked_path(('a', 'c')) == False
graph.add_marked_arrowhead(('b', 'c'))
assert graph.has_marked_path(('a', 'c')) == True
assert graph.get_nodes_of_edges() == set({'a', 'b', 'c'})
def test_longer_marked_path_exists():
# a -*> b -*> c -*> d
# \ /
# \ /
# \ /
# ------
graph = MarkedPatternGraph(nodes=['a', 'b', 'c', 'd'])
graph.add_undirected_edge(('a', 'b'))
graph.add_undirected_edge(('b', 'c'))
graph.add_undirected_edge(('c', 'd'))
graph.add_undirected_edge(('a', 'd'))
graph.add_marked_arrowhead(('a', 'b'))
graph.add_marked_arrowhead(('b', 'c'))
graph.add_marked_arrowhead(('c', 'd'))
assert graph.has_marked_path(('d', 'c')) == False
