def test_join():
list = SingleLinkedList()
list2 = SingleLinkedList()
list.join(list2)
assert list.isEmpty()
list.prepend(1).prepend(2).prepend(3)
list2.prepend(4).prepend(5).prepend(6)
list.join(list2)
assert list.head() == 6
assert list.size() == 6
def test_average():
list = SingleLinkedList().append(1).append(2).append(3).append(4)
assert average(list) == 2.5
list2 = SingleLinkedList().prepend(5).prepend(10).prepend(50).prepend(
100).prepend(500)
assert average(list2) == 133.0
assert average(list.join(list2))
