How to define the site to be used in BrowserTestBase on a multisite? I am working on a multi site where there is no database defined in the default directory, so whenever I run a Functional test extending BrowserTestBase I get the following error: 

copy(/var/www/drupal-int/docroot/sites/default/default.settings.php): failed to open stream: No such file or directory


I'm not really sure why the files were removed in the first place and I don't want to add them back in there in case there was a good reason for removing them. Is there a way to define the site to use for the test?

My simple test:

&lt;?php

namespace Drupal\Tests\my_module\Functional;

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

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

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

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

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

  /**
   * Tests that the home page loads with a 200 response.
   */
  public function testLoad() {
    $this-&gt;drupalGet(Url::fromRoute('&lt;front&gt;'));
    $this-&gt;assertResponse(200);
  }

}
None of your existing sites are used during a fonctionnal test, drupal creates a fresh install defined by your static attribute $modules and the setUp() method.

So, you should get the default.settings.php file back (and create a /sites/simpletest folder)