无法对DB播种器执行集成测试 - 错误：在null

Question

我正在尝试为我的db浏览器编写集成测试，但它似乎没有返回该播种器的实例。所以它无法执行

当我调试它时，$ adminUserSeeder显示以下内容

这是我的测试

 namespace Tests\Unit\user;
use AdminUserSeeder;
use App\Test;
use Illuminate\Foundation\Testing\DatabaseTransactions;
use PHPUnit\Framework\TestCase;

class AdminSeederTest extends TestCase
{
    use DatabaseTransactions;

    public function setUp()
    {
        parent::setUp();
    }

    public function testRun()
    {
        $adminUserSeeder = new AdminUserSeeder();
        $adminUserSeeder->run();
        $this->assertDatabaseHas('users', ['name' =>  'admin']);
    }

}

这是我的播种机课程

使用Illuminate \ Database \ Seeder;

class AdminUserSeeder extends Seeder
{

    public function run()
    {
     $user = (new App\User)->where('name','admin')->first();
      if($user)
         {
             $user->delete();
         }
        factory(App\User::class,'admin')->create();
    }
}

添加了堆栈跟踪

 /laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1138
/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1104
/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:936
/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:880
/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:843
/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1477
/database/seeds/AdminUserSeeder.php:10
/tests/Unit/AdminSeederTest.php:21