Custom TWiG template for SELECT element I have created twig template to override SELECT element for SELECT-element in user exposed filters. 

However I can't figure out how to make it only work within a specific view "testing" ?
You should implements hook_theme_suggestions_HOOK_alter() to add a suggestion for 'select' element. Then create a new twig template in THEME/templates folder with the name 'select--$view_id.html.twig'.

Example code:

function HOOK_theme_suggestions_select_alter(array &amp;$suggestions, array $variables) {
  $routeObject = \Drupal::routeMatch()-&gt;getRouteObject();
  $view_id = $routeObject-&gt;getDefault('view_id');
  $display_id = $routeObject-&gt;getDefault('display_id');

  if (!empty($view_id)) {
    $suggestions[] = 'select__' . $view_id;

    if (!empty($display_id)) {
      $suggestions[] = 'select__' . $view_id . '_' . $display_id;
    }
  }
}