How do I use filter `testimonials_widget_get_testimonial_html`?

See How do I customize my testimonial list and widget output? for more details.

add_filter( 'testimonials_widget_get_testimonial_html', 'my_testimonials_widget_get_testimonial_html', 10, 13 );

function my_testimonials_widget_get_testimonial_html( $html, $testimonial, $atts, $is_list, $is_first, $widget_number, $div_open, $image, $quote, $cite, $extra, $bottom_text, $div_close ) {
    // do stuff… see Testimonials_Widget::get_testimonials_html for default processing
    if ( is_page( 437 ) ) {
        $source                 = '';
        if ( ! empty( $testimonial['testimonial_source'] ) )
            $source             = '<h3>' . $testimonial['testimonial_source'] . '</h3>';

        $html                   = $div_open
            . $source
            . $image
            . $quote
            // . $cite
            // . $extra
            // . $bottom_text
            . $div_close;
        return $html;
    } elseif ( false && $is_list ) {
        return '<li>' . $image . $testimonial['testimonial_title'] . '</li>';
    } else {
        return $html;
    }
}