why is my unittest not running

I am writing a unites to test my codes but in the end it says ran 0 tests. This is my code for my unites:

import roman1
import roman2
import unittest

class KnownValues(unittest.TestCase):
    known_values =  ((1, 'I'),
                     (2, 'II'),
                     (3, 'III'),
                     (4, 'IV'),
                     (5, 'V'))
def test_to_roman_values(self):
    for integer, numeral in self.known_values:
        result = roman1.to_roman(integer)
        self.assertEqual(numeral, result)

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

But it says ran 0 tests in 0 seconds. I was able to run another unites I wrote fine and the setup is basically the same. Is something wrong in my code? I am using python from mac OS X