def test_add_parent(self):
dp = Node(label="DP")
d = Node(label="D", value="the")
dp.add_child(d)
n = Node(label="N", value="cactus")
dp.add_child(n)
np = Node(label="NP")
n.add_parent(np)
self.assertIn(np, dp.children)
self.assertEqual(np, n.parent)
self.assertNotIn(n, dp.children)
def test_add_parent_replacing_root(self):
n = Node(label="N", value="cacti")
np = Node(label="NP")
with self.assertRaises(AssertionError):
n.add_parent(np)
