def test_centers(self):
self.assertEqual(centers(self.tree_one), {1, 3})
self.assertEqual(centers(self.tree_two), {1, 2})
tree = Graph()
tree.add_edge(1, 2)
tree.add_edge(2, 3)
self.assertEqual(centers(tree), {2, })
def test_centers_empty_tree(self):
tree = Graph()
self.assertEqual(centers(tree), set())
def test_centers_one_node_tree(self):
tree = Graph()
tree.add_node(1)
self.assertEqual(centers(tree), {1, })
