def test_2(self):
     self.assertEqual(factorial_digit_sum(2), 2)
 def test_1(self):
     self.assertEqual(factorial_digit_sum(1), 1)
 def test_10(self):
     self.assertEqual(factorial_digit_sum(10), 27)
 def test_project_euler_input(self):
     self.assertEqual(factorial_digit_sum(100), 648)
 def test_4(self):
     self.assertEqual(factorial_digit_sum(4), 6)