def test_return_desired_value():
tree = BinaryTree()
node1 = Node(1)
node2 = Node(3)
node3 = Node(5)
node1.left = node2
node1.right = node3
tree.root = node1
actual = tree.find_max_value()
expected = 5
assert actual == expected
def test_nothing_in_tree():
tree = BinaryTree()
actual = tree.find_max_value()
expected = None
assert actual == expected