public function testRandomStrings()
{
$user = new User();
$last = '';
for ($i = 0; $i < 500; $i++) {
$now = $user->getRandomString();
if ($now === $last) {
throw new \UnexpectedValueException("Two random strings are the same, [{$now}], [{$last}].");
}
$last = $now;
}
}