def test_dll_add_head():
test_dll = DLL()
test_dll.add_head(1)
assert test_dll.head.data == 1
assert test_dll.tail.data == 1
test_dll.add_head(2)
assert test_dll.head.data == 2
assert test_dll.tail.data == 1
test_dll.add_head(3)
assert test_dll.head.data == 3
assert test_dll.tail.data == 1
