def test_dupicate_nonempty(self):
stack = Stack([True])
stack.dup()
assert len(stack) is 2 and stack[-1]
def test_stack_opper_dup_add(self):
stack = Stack()
stack.append(1)
stack.dup()
stack.math.add()
assert len(stack) is 1 and stack[-1] is 2
def test_duplicate_empty(self):
stack = Stack()
stack.dup()
assert stack.isempty() is True