WP -- Get posts by category?

I'm using this in my page template to get posts by their category:

<?php 
        if (is_page(19)){
            ?>
            <ul>
            <?php
                global $post;
                $args = array( 'category' => 'Testimonial' );
                $myposts = get_posts( $args );
                foreach( $myposts as $post ) :  setup_postdata($post); ?>
                    <li class="testimonial"><?php the_content(); ?></li><br/>
                <?php endforeach; ?>
            </ul>
        <?php } ?>

but it's retrieving all posts instead. Not just the ones labeled Testimonial. Any idea what I'm doing wrong?