def test_prev_node_of_min(self):
"""
test the following binary search tree
3
/
2
/
1 <-- get prev node of 1
"""
bst = BinarySearchTree()
bst.insert(3)
bst.insert(2)
node = bst.insert(1)
self.assertEqual(bst.prev(node), None)
def test_prev_node_has_left_subtree(self):
"""
test the following binary search tree
4 <-- get prev node of 4
/
2
/ \
1 3
"""
bst = BinarySearchTree()
node = bst.insert(4)
bst.insert(2)
bst.insert(1)
expected_prev = bst.insert(3)
self.assertEqual(bst.prev(node), expected_prev)