Social Proof Slider - Show all testimonials in a UL list

functions.php

<?php

/* 
* This code will create a new 'list-testimonials' shortcode, which will show all testimonials in a UL list.
* Add this to your theme's functions.php file.
*/

// Add Shortcode
add_shortcode( 'list-testimonials', 'spslider_list_testimonials' );

// Shortcode function
function spslider_list_testimonials(){

    // Set the output var
    $return = '';

	// WP Query arguments
	$args = array(
		'post_type'              => array( 'socialproofslider' ),
		'post_status'            => array( 'published' ),
		'posts_per_page'         => '-1',
		'order'                  => 'DESC',
		'orderby'                => 'date',
	);

    // Query for WP items
    $query = new WP_Query( $args );


    if ( $query->have_posts() ) :

        $return .= '<ul class="testimonials-list">';

        while ( $query->have_posts() ) : $query->the_post();

            // Get the post ID
            $postid = get_the_ID();

            // Get meta values
            $meta = get_post_custom( $postid );

            // Get the Testimonial Text
            $testimonialtext = '';
            $testimonialtext = $meta['socialproofslider_testimonial_text'][0];

            // Get option for Smart Quotes
            $surroundWithQuotes = get_option('social_proof_slider_surroundquotes');

            // Set the Smart Quotes string
            $quoteTextStart = "";
            $quoteTextEnd = "";
            if( $surroundWithQuotes ){
                $quoteTextStart = "“";
                $quoteTextEnd = "”";
            }

            // Set default value for showing Featured Image
            $showThisFeaturedImage = true;  // default

            // Check if Featured Image exists
            if ( function_exists('has_post_thumbnail') && has_post_thumbnail( $postid ) ) {
                $thumb = wp_get_attachment_image_src( get_post_thumbnail_id( $postid ), 'social-proof-slider' );
                if ( !$thumb[0] ){
                    // no src, do nothing
                    $showThisFeaturedImage = false;
                } else {
                    $theFeaturedImage = $thumb[0];
                }
            }

            $return .= '<li class="testimonial-item item-'.$postid.'">';

            // Output the Featured Image
            if ( $showThisFeaturedImage ) {
                $return .= '<div class="testimonial-author-img-wrap">';
                $return .= '<div class="testimonial-author-img">';
                $return .= '<img src="' . $theFeaturedImage . '" class="client-image" />';
                $return .= '</div>';
                $return .= '</div>';
            }

            // Output the Testimonial Text
            $return .= '<div class="quote">';
            $return .= $quoteTextStart . html_entity_decode( $testimonialtext ) . $quoteTextEnd;
            $return .= '</div>';

            $return .= '</li>';

        endwhile;

        $return .= '</ul>';

    endif;

	// Reset the query
    wp_reset_postdata();

	// Output everything
    return $return;

}