def test_eval_with_node(self):
node = RootNode()
combination = CombinationNode()
combination.append(PrimitiveNode(add))
combination.append(PrimitiveNode(1))
combination.append(PrimitiveNode(2))
node.append(combination)
assert 3 == node.eval()
def test_eval_without_node(self):
node = RootNode()
assert node.eval() is None