Project Euler Problem#30

#python program to sum of all the numbers that can be written as the sum of fifth powers of their digits
import unittest

def digit_sum(power):
    if type(power)!=int or power<2:
        return None
    list1=[]
    for i in range(2,1000000):
        num=0
        for j in str(i):
            num+=(int(j))**power
        if num==i:
            list1.append(i)
    return sum(list1)

print(digit_sum(5))

class TestCases(unittest.TestCase):

    def test_digit_sum(self):
        self.assertEqual(digit_sum(-5),None)
        self.assertEqual(digit_sum(2),0)
        self.assertEqual(digit_sum(4),19316)
        self.assertEqual(digit_sum("5"),None)
        self.assertEqual(digit_sum(4.5),None)


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