def test_product_of_two_digit_numbers(self):
"""
the largest palindrome which is the product of 2, 2 digit
numbers is 9009: 99 x 91
"""
self.assertEqual(largest_palindrome(2), 9009)
def test_product_of_four_digit_numbers(self):
"""
the largest palindrome which is the product 2, 4 digit
numbers is 99000099
"""
self.assertEqual(largest_palindrome(4), 99000099)