def test_exists(self):
""" Tests for membership.
"""
sll = SinglyLinkedList()
node1, node2, node3 = Node(1), Node(2), Node(3)
sll.append(node1)
sll.append(node2)
sll.append(node3)
self.assertTrue(sll.exists(node1))
self.assertTrue(sll.exists(node2))
self.assertTrue(sll.exists(node3))
self.assertFalse(sll.exists(Node(4)))
# Membership is based on object identity, not value
self.assertFalse(sll.exists(Node(1)))
