def test_noe_add_parent():
n1 = Node("Node1")
n2 = Node("Node2")
n3 = Node("Node3")
n1.add_parent(n2)
n1.add_parent(n3)
n2.add_parent(n3)
## check n1 prperties.
assert (n2 in n1.parents) and (n3 in n1.parents)
assert n1.children == []
## check n2 properties
assert (n3 in n2.parents)
assert (n1 in n2.children)
## checck n3 properties
assert (n2 in n3.children) and (n1 in n3.children)
assert n3.parents == []
