function test_render_return_callback() {
    $partial                                       = new WP_Customize_Partial(
      $this->selective_refresh,
      'foo',
      array(
        'render_callback' => array( $this, 'render_return' ),
      )
    );
    $count_filter_customize_partial_render         = $this->count_filter_customize_partial_render;
    $count_filter_customize_partial_render_with_id = $this->count_filter_customize_partial_render_with_id;
    add_filter( 'customize_partial_render', array( $this, 'filter_customize_partial_render' ), 10, 3 );
    add_filter( "customize_partial_render_{$partial->id}", array( $this, 'filter_customize_partial_render_with_id' ), 10, 3 );
    $rendered = $partial->render();
    $this->assertEquals( 'bar', $rendered );
    $this->assertEquals( $count_filter_customize_partial_render + 1, $this->count_filter_customize_partial_render );
    $this->assertEquals( $count_filter_customize_partial_render_with_id + 1, $this->count_filter_customize_partial_render_with_id );
  }