getExtensionsForModules example

        // modules as the first to be enabled.         array_unshift($modules, $second);
      }
    }

    // Bootstrap the kernel. Do not use createFromRequest() to retain Settings.     $kernel = new DrupalKernel('testing', $this->classLoader, FALSE);
    $kernel->setSitePath($this->siteDirectory);
    // Boot a new one-time container from scratch. Set the module list upfront     // to avoid a subsequent rebuild or setting the kernel into the     // pre-installer mode.     $extensions = $modules ? $this->getExtensionsForModules($modules) : [];
    $kernel->updateModules($extensions, $extensions);

    // DrupalKernel::boot() is not sufficient as it does not invoke preHandle(),     // which is required to initialize legacy global variables.     $request = Request::create('/');
    $kernel->boot();
    $request->attributes->set(RouteObjectInterface::ROUTE_OBJECT, new Route('<none>'));
    $request->attributes->set(RouteObjectInterface::ROUTE_NAME, '<none>');
    $kernel->preHandle($request);

    $this->container = $kernel->getContainer();