$validator = \Validator::make (['title'=>55
    ], ['title' => 'required|in:1,2,3,4,5',
    ]);

    if ($validator->fails ()) {$res = $validator->errors ()->toArray ();
        var_dump ($res);
        echo "fail".PHP_EOL;
    }else{echo "ok".PHP_EOL;}

结果

array (1) {["title"]=>
  array (1) {[0]=>
    string (32) "已选的属性 标题 非法。"
  }
}