Laravel phpunit多个数据库测试未运行

'connections' => [
    'mysql' => [
        'driver' => 'mysql',
        'host' => env('DB_HOST', '127.0.0.1'),
        'port' => env('DB_PORT', '3306'),
        'database' => env('DB_DATABASE', 'forge'),
        'username' => env('DB_USERNAME', 'forge'),
        'password' => env('DB_PASSWORD', ''),
        'charset' => 'utf8mb4',
        'collation' => 'utf8mb4_unicode_ci',
        'prefix' => '',
        'strict' => true,
        'engine' => null,
    ],
    'second_db' => [
        'driver' => 'mysql',
        'host' => env('SECOND_DB_HOST', '127.0.0.1'),
        'port' => env('SECOND_DB_PORT', '3306'),
        'database' => env('SECOND_DB_DATABASE', 'forge'),
        'username' => env('SECOND_DB_USERNAME', 'forge'),
        'password' => env('SECOND_DB_PASSWORD', ''),
        'charset' => 'utf8mb4',
        'collation' => 'utf8mb4_unicode_ci',
        'prefix' => '',
        'strict' => true,
        'engine' => null,
    ],
],

use Illuminate\Foundation\Testing\DatabaseTransactions;

class ExampleTest extends TestCase
{
    use DatabaseTransactions;

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

        // 使用默认的mysql连接
        $this->app['config']->set('database.default', 'mysql');
    }

    public function testExample()
    {
        // 测试代码
    }

    public function testSecondDatabase()
    {
        // 使用second_db连接进行测试
        $this->app['config']->set('database.default', 'second_db');

        // 测试代码
    }
}