LaravelのPHPUnitでWithFakerなどのTraitが動かない

当初以下のようなコードを書いていたのだが、

namespace Tests\Unit\Repositories;

use PHPUnit\Framework\TestCase;
use App\Models\User;
use App\Constants;
use App\Repositories\PgSql\UserRepository;
use Illuminate\Foundation\Testing\RefreshDatabase;
use Illuminate\Foundation\Testing\WithFaker;

class UserRepositoryTest extends TestCase
{
    use WithFaker, RefreshDatabase;

    protected function setUp(): void
    {
        parent::setUp();
    }

    // expected 1 user is found, not others.
    public function testFindUserByAuthInfo()
    {
        $repo = new UserRepository();
        // findable
        $user = factory(User::class)->create([
            'id' => $this->faker->uuid,
            'password' => password_hash($this->faker->password(), PASSWORD_BCRYPT),
            'account_id' => 1,
            'email' => $this->faker->email,
        ]);

実行すると

1) Tests\Unit\Repositories\UserRepositoryTest::testFindUserByAuthInfo
Trying to get property 'uuid' of non-object

と$this->fakerでFakerがインスタンス化できていない模様

散々調べた挙げ句、結局
use PHPUnit\Framework\TestCase;
を
use Tests\TestCase;
にしたら直ったというお話。