public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ) {
    // Note that our top/children/grandchildren arrays are 1-indexed.

    // Create top-level pages.
    $num_posts = 5;
    foreach ( range( 1, $num_posts ) as $i ) {
      $p = $factory->post->create_and_get(
        array(
          'post_type'  => 'page',
          'post_title' => sprintf( 'Top Level Page %d', $i ),
        )
      );

      self::$top[ $i ]  = $p;
      self::$post_ids[] = $p->ID;
    }

    // Create child pages.
    $num_children = 3;
    foreach ( self::$top as $top => $top_page ) {
      foreach ( range( 1, $num_children ) as $i ) {
        $p = $factory->post->create_and_get(
          array(
            'post_type'   => 'page',
            'post_parent' => $top_page->ID,
            'post_title'  => sprintf( 'Child %d', $i ),
          )
        );

        self::$children[ $top ][ $i ] = $p;
        self::$post_ids[]             = $p->ID;
      }
    }

    // Create grand-child pages for the third and fourth top-level pages.
    $num_grandchildren = 3;
    foreach ( range( 3, 4 ) as $top ) {
      foreach ( self::$children[ $top ] as $child => $child_page ) {
        foreach ( range( 1, $num_grandchildren ) as $i ) {
          $p = $factory->post->create_and_get(
            array(
              'post_type'   => 'page',
              'post_parent' => $child_page->ID,
              'post_title'  => sprintf( 'Grandchild %d', $i ),
            )
          );

          self::$grandchildren[ $top ][ $child ][ $i ] = $p;
          self::$post_ids[]                            = $p->ID;
        }
      }
    }
  }