Laravel のテストであるクラスのプロパティをテストから書き換えて初期化するには

<?php

namespace App\Services;

class SomeService
{
    private $config;

    public function __construct()
    {
        $this->config = config('services.some.config');
    }

    public function doSomething()
    {
        return $this->config;
    }
}

<?php

namespace Tests\Feature\Services;

use App\Services\SomeService;
use Tests\TestCase;

class SomeServiceTest extends TestCase
{
    public function testDoSomethingInGeneralEnvironment()
    {
        $service = app(SomeService::class);

        $this->assertEquals('hoge', $service->doSomething());
    }

    public function testDoSomethingInSpecialEnvironment()
    {
        $service = new class extends SomeService {
            public function __construct()
            {
                $class = new \ReflectionClass(SomeService::class);
                $property = $class->getProperty('config');
                $property->setAccessible(true);
                $property->setValue($this, env('SOME_SERVICE_CONFIG_OVERWRITTEN'));
            }
        };

        $this->assertEquals('fuga', $service->doSomething());
    }
}

    'some' => [
        'config' => env('SOME_SERVICE_CONFIG'),
    ],

SOME_SERVICE_CONFIG=hoge
SOME_SERVICE_CONFIG_OVERWRITTEN=fuga