"""
Given a list of integers and a single sum value,
return the first two values (parse from the left please)
in order of appearance that add up to form the sum.
sum_pairs([11, 3, 7, 5],         10)
#              ^--^      3 + 7 = 10
== [3, 7]

sum_pairs([4, 3, 2, 3, 4],         6)
#          ^-----^         4 + 2 = 6, indices: 0, 2 *
#             ^-----^      3 + 3 = 6, indices: 1, 3
#                ^-----^   2 + 4 = 6, indices: 2, 4
#  * entire pair is earlier, and therefore is the correct answer
== [4, 2]

sum_pairs([0, 0, -2, 3], 2)
#  there are no pairs of values that can be added to produce 2.
== None/nil/undefined (Based on the language)

sum_pairs([10, 5, 2, 3, 7, 5],         10)
#              ^-----------^   5 + 5 = 10, indices: 1, 5
#                    ^--^      3 + 7 = 10, indices: 3, 4 *
#  * entire pair is earlier, and therefore is the correct answer
== [3, 7]
Negative numbers and duplicate numbers can and will appear.

NOTE: There will also be lists tested of lengths
upwards of 10,000,000 elements. Be sure your code doesn't time out.
"""
def sum_pairs(ints, s):
    pass

def assert_eq_or_none(tfunc_call_result, check_against, text):
    if check_against is None:
        assert tfunc_call_result is None, text
    else:
        assert tfunc_call_result == check_against, text

if __name__ == '__main__':
    args_cases = [
        ([1, 4, 8, 7, 3, 15], 8),
        ([1, -2, 3, 0, -6, 1], -6),
        ([20, -13, 40], -7),
        ([1, 2, 3, 4, 1, 0], 2),
        ([10, 5, 2, 3, 7, 5], 10),
        ([4, -2, 3, 3, 4], 8),
        ([0, 2, 0], 0),
        ([5, 9, 13, -3], 10),
        ([1] + [10 for x in range(9_999_998)] + [1], 2),
    ]
    test_cases = [
        ([1, 7], "Basic: {} should return [1, 7] for sum = 8"),
        ([0, -6], "Negatives: {} should return [0, -6] for sum = -6"),
        (None, "No Match: {} should return None for sum = -7"),
        ([1, 1], "First Match From Left: {} should return [1, 1] for sum = 2 "),
        ([3, 7], "First Match From Left REDUX!: {} should return [3, 7] for sum = 10 "),
        ([4, 4], "Duplicates: {} should return [4, 4] for sum = 8"),
        ([0, 0], "Zeroes: {} should return [0, 0] for sum = 0"),
        ([13, -3], "Subtraction: {} should return [13, -3] for sum = 10"),
        ([1, 1], "10m elements list, [1, 10, 10 ... 10, 1], should return [1, 1] for sum = 2")
    ]
    for args, case in zip(args_cases, test_cases):
        assert_eq_or_none(sum_pairs(*args), case[0], case[1].format(args[0]))