def _check(self, source):
        for nbytes in range(17, 25):
            s = source(nbytes)
            self.assertEqual(len(s), nbytes)
            s2 = source(nbytes)
            self.assertEqual(len(s2), nbytes)
            # This is crude but hey
            self.assertNotEqual(s2, s)
Find a user by name. Return ``None`` if no such user exists.
dataset/ETHPy150Open twisted/twisted/twisted/test/test_randbytes.py/SecureRandomTestCaseBase._check--crossover with--dataset/ETHPy150Open mblayman/markwiki/markwiki/storage/user.py/UserStorage.find_by_name