def test_merge_with_one_shorter_valid(one_four_ll, a_b_cap_ll):
"""
test merge list function where second list is shorter
"""
merge_lists(one_four_ll, a_b_cap_ll)
# assert one_four_ll.head.val == 1
assert one_four_ll.head._next._next._next._next.val == 3
def test_merge_with_one_empty_list_switched(one_four_ll, empty_ll):
"""
test merge list function with one empty linked list and one full linked list
"""
merge_lists(empty_ll, one_four_ll)
assert one_four_ll.head.val == 1
assert one_four_ll.head._next.val == 2
def test_merge_list_valid_switched(one_four_ll, a_d_ll):
"""
test merge list function to ensure two lists when passed in are 'zipped' together
"""
merge_lists(a_d_ll, one_four_ll)
assert a_d_ll.head._next.val == 'a'
assert a_d_ll.head.val.val == 1
def test_merge_list_valid_switched_extended(one_four_ll, a_d_ll):
"""
test merge list function to ensure two lists when passed in are 'zipped' together. traverse further along to check alternation
"""
merge_lists(a_d_ll, one_four_ll)
assert a_d_ll.head._next._next._next.val == 'b'
def test_merge_list_valid(one_four_ll, a_d_ll):
"""
test merge list function to ensure two lists when passed in are 'zipped' together
"""
merge_lists(one_four_ll, a_d_ll)
assert str(one_four_ll.head.val) == 'a'