def test_no_duplicates(self):
self.assertEqual(first_index([1, 2, 3, 4, 5, 6, 7, 8, 9], 3), 2)
def test_all_duplicates(self):
numbers = [3, 3, 3, 3, 3, 3, 3, 3, 3]
self.assertEqual(first_index(numbers, 3), 0)
def test_not_found(self):
numbers = [1, 2, 4, 5, 6, 7, 8, 9]
self.assertEqual(first_index(numbers, 3), None)
def test_some_duplicates(self):
numbers = [1, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 5, 6, 7, 8, 9]
self.assertEqual(first_index(numbers, 3), 3)