Display All Custom Fields For a Post

Hi there,

I’m trying to display all Custom Fields for a post but I don’t know how to do that. The code below is showing only one.

              <div class="testimonial">
              <?php 
                $client_testimonial = get_post_meta( get_the_ID(), 'Testimonial', true);
                if( ! empty( $client_testimonial ) ) {
                   echo '<div>' . $client_testimonial . '</div>';
                }
               ?>
               </div>

Appreciate the help. Thanks!