File upload form validation is not working in laravel 5.1?

I am using form validation to upload file in laravel 5.1,

  class FileUploadRequest extends Request {

   public function rules() {
    return ['file' => 'required', 'max:2048', 'mimes:pdf,png,jpeg,jpg'];
}

  public function upload(FileUploadRequest $request) {
  }

But it is not validating both size and mime.. what is wrong with me?

via Chebli Mohamed