How do I customize my testimonial single output

Step-by-step guide

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

add_filter( 'testimonials_widget_testimonial_html_single', 'my_testimonials_widget_testimonial_html_single', 10, 3 );

function my_testimonials_widget_testimonial_html_single( $content, $testimonial, $atts ) {
    // see Testimonials_Widget::get_testimonials_html for default processing
    
    // do stuff…

    return $content;
}