How can I run functional tests from a custom module to test one specific mult-site instance?

Question

I have tried to do a simple test of a module located on a sub site (Drupal multisite), but when the test looks for the module to activate it, it can not be found, if I move the module from the sub site to the modules folder that it is at the root of the installation if it finds it.

Is it possible to do the tests from the subsite? or do I necessarily have to move them to the root folder?

namespace Drupal\Tests\gonza_multiple\Functional;

use Drupal\Core\Url;
use Drupal\Tests\BrowserTestBase;

/**
 * Simple test to ensure that main page loads with module enabled.
 *
 * @group gonza_multiple
 */
class LoadTest extends BrowserTestBase {

  /**
   * Modules to enable.
   *
   * @var array
   */
  public static $modules = ['gonza_multiple'];

  /**
   * A user with permission to administer site configuration.
   *
   * @var \Drupal\user\UserInterface
   */
  protected $user;

  /**
   * {@inheritdoc}
   */
  protected function setUp() {
    parent::setUp();
    $this->user = $this->drupalCreateUser(['administer site configuration']);
    $this->drupalLogin($this->user);
  }

  /**
   * Tests that the home page loads with a 200 response.
   */
  public function testLoad() {
    $this->drupalGet(Url::fromRoute('<front>'));
    $this->assertSession()->statusCodeEquals(200);
  }

}