关于 43 节的遗漏?

SubscribeToThreadsTest中的两个测试文中交代的有些模糊，跟到最后测试无法全部通过，参照源码修改如下后与教程效果同步

/** @test */
public function a_user_can_subscribe_to_threads()
{
    $this->signIn();
    // Given we have a thread...
    $thread = create('App\Thread');
    // And the user subscribes to the thread...
    $this->post($thread->path() . '/subscriptions');

    $this->assertCount(1, $thread->fresh()->subscriptions);
}

/** @test */
public function a_user_can_unsubscribe_from_threads()
{
    $this->signIn();
    $thread = create('App\Thread');
    // 这里原文笔记中忘记了一行，虽然测试不会报错，但是却不符合业务逻辑，源码中是有下面这一行，逻辑更加合理
    $thread->subscribe();
    $this->delete($thread->path() . '/subscriptions');
    $this->assertCount(0, $thread->subscriptions);
}