public function set_up() {
    parent::set_up();
    require_once ABSPATH . WPINC . '/class-wp-customize-manager.php';

    $user_id = self::factory()->user->create(
      array(
        'role' => 'administrator',
      )
    );
    if ( is_multisite() ) {
      grant_super_admin( $user_id );
    }

    wp_set_current_user( $user_id );

    global $wp_customize;
    $this->wp_customize = new WP_Customize_Manager();
    $wp_customize       = $this->wp_customize;

    do_action( 'customize_register', $this->wp_customize );
    $this->setting = new WP_Customize_Custom_CSS_Setting( $this->wp_customize, 'custom_css[' . get_stylesheet() . ']' );
    $this->wp_customize->add_setting( $this->setting );
  }