def test_username_pass_when_valid(self):
try:
validate_username('a.valid_username-123')
except:
self.fail('Valid username should not raise an exception')
def test_username_raises_error_when_it_contains_uppercase_letters(self):
with self.assertRaises(ValueError):
validate_username('INVALIDUSERNAME')
def test_username_raises_error_when_it_contains_special_characters(self):
with self.assertRaises(ValueError):
validate_username('invalid@username')
