Display just one testimonial

I am calling:

tbtestimonial('random');

and expected just one testimonial, but all seem to be output.

I looked in tb-testimonials.php line 736 and assumed that:

$q = new WP_Query( array( 'post_type' => 'testimonial', 'post_status' => 'publish', 'orderby' => 'rand', 'showposts' => 1 ) );

would only output one due to 'showposts' => 1 but I assume my knowledge of WP is not correct.

(saw this on the WP class reference:

Display one random post:
$query = new WP_Query( array ( 'orderby' => 'rand', 'posts_per_page' => '1' ) );

[‘posts_per_page’ is preferred to ‘showposts’]

Or is there another way to achieve this with tbtestimonial?

Thanks