def test_neighbors(self):
"""Test root()."""
# Create [{1, 2}, {2}, set()].
a_graph = DirectedGraph()
a_graph.connect(0, 1)
a_graph.connect(0, 2)
a_graph.connect(1, 2)
# Check neighbors on existing vertices.
self.assertEqual(a_graph.neighbors(0), {1, 2})
self.assertEqual(a_graph.neighbors(1), {2})
self.assertEqual(a_graph.neighbors(2), set())
# Check neighbors on non-existing vertices.
self.assertEqual(a_graph.neighbors(3), set())
self.assertEqual(a_graph.neighbors(4), set())
def test_initialization(self):
"""Test public methods on an empty union."""
# Create [].
an_empty_graph = DirectedGraph()
self.assertEqual(an_empty_graph.n_vertices(), 0)
self.assertEqual(an_empty_graph.connected(0, 0), False)
self.assertEqual(an_empty_graph.connected(0, 1), False)
self.assertEqual(an_empty_graph.neighbors(0), set())
