Respect\Validation\Rules\Mimetype::validate PHP Method

    public function validate($input)
    {
        if ($input instanceof SplFileInfo) {
            $input = $input->getPathname();
        }
        if (!is_string($input)) {
            return false;
        }
        if (!is_file($input)) {
            return false;
        }
        return $this->fileInfo->file($input) == $this->mimetype;
    }

 public function testShouldInvalidateWhenItIsNotAValidFile()
 {
     $rule = new Mimetype('application/octet-stream');
     $this->assertFalse($rule->validate(__DIR__));
 }