控制器中未定义的变量 我正在尝试在 laravel 中使用 phpunit 进行测试

我正在尝试学习单元测试的基础知识，我正在使用phpunit和laravel。

这是我的控制器

胖控制器.php

class FatController extends BaseController {
    public $result;
    public function __construct($result)
    {
        $this->result = $result;
    }
    public function getResult()
    {
        return $this->$result;
    }
}

和测试类

胖控制器测试.php

class FatControllerTest extends TestCase {
    /**
     * A basic functional test example.
     * @return void
     */
    public $test;
    public function setUp()
    {
        parent::setUp();
        $this->test = new FatController('100%');
    }
    public function testResult()
    {
        $result = $this->test->getResult();
        $this->assertTrue($result == '100%', 'message');
    }
}

据我所知，当测试运行时，它应该创建一个新的变量$test它等于一个值为 100% 的 FatController 的新实例

然后它运行$test FatController 方法 getResult，该方法应返回构造函数定义为"100%"的$result

但是当测试运行时，我得到这个

PHP Warning:  Uncaught exception 'ErrorException' with message 'Undefined variable: result' in /Users/irish/Dropbox/www/youtube/app/controllers/FatController.php:15
Stack trace:
#0 /Users/irish/Dropbox/www/youtube/app/controllers/FatController.php(15): Illuminate'Exception'Handler->handleError(8, 'Undefined varia...', '/Users/irish/Dr...', 15, Array)
#1 /Users/irish/Dropbox/www/youtube/app/tests/FatControllerTest.php(22): FatController->getResult()
#2 [internal function]: FatControllerTest->testResult()
#3 /Users/irish/.composer/vendor/phpunit/phpunit/PHPUnit/Framework/TestCase.php(983): ReflectionMethod->invokeArgs(Object(FatControllerTest), Array)
#4 /Users/irish/.composer/vendor/phpunit/phpunit/PHPUnit/Framework/TestCase.php(838): PHPUnit_Framework_TestCase->runTest()
#5 /Users/irish/.composer/vendor/phpunit/phpunit/PHPUnit/Framework/TestResult.php(648): PHPUnit_Framework_TestCase->runBare()
#6 /Users/irish/.composer/vendor/phpunit/phpunit/PHPUnit/Framework/TestCase.php(783): PHPUnit_Framework_TestResult->run(Object(Fat in /Users/irish/Dropbox/www/youtube/app/controllers/FatController.php on line 15
PHP Fatal error:  Cannot access empty property in /Users/irish/Dropbox/www/youtube/app/controllers/FatController.php on line 15

所以我知道$result没有被定义为任何东西，当getResult尝试返回它时会导致错误，但我不知道我做错了什么