exception_raises.py

#/usr/bin/python3.5
import unittest

def add(x, y):
    if x == y:
        raise ValueError('X cannot equal Y because reasons')
    else:
        return x + y

class TestyTesterson(unittest.TestCase):
    def test_add_fails_duplicates(self):
        add(5,5)
        with self.assertRaises('ValueError'):
            pass

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