main.py

def binary_search(needle, haystack):
    start, end = 0, len(haystack)-1
    while start < end:
        pivot_idx = (start + end) // 2
        pivot = haystack[pivot_idx]
        if needle == pivot:
            return True
        if pivot_idx == start:
            # edge case -- I'm sure a better algorithm
            # would write this into the while condition
            break
        if needle < pivot:
            end = pivot_idx
        else:
            start = pivot_idx
    return False

test_main.py

import unittest
from main import binary_search

class Tester(unittest.TestCase):
    
    def test_sorted_lists(self):
        true_cases = [(3, [1, 3, 4, 5, 6, 7]),
                      ("s", ['a','b','s','q'])]
        false_cases = [(2, [1, 3, 4, 5, 6, 7]),
                       ('something', ['a', 'list', 'of', 'test', 'values'])]
        for case in true_cases:
            needle, haystack = case
            self.assertTrue(binary_search(needle, haystack))
        for case in false_cases:
            needle, haystack = case
            self.assertFalse(binary_search(needle, haystack))
    
    def test_unsorted_list(self):
        test_case = [('something', ['an', 'unsorted', 'list'])]
        for case in test_case:
            needle, haystack = case
            self.assertFalse(binary_search(needle, haystack))

if __name__ == "__main__":
    unittest.main()