Custom Post type content within a slider

Since WP loaded with jQuery by default, you might be able to modify this script http://www.jqueryscript.net/rotator/Simple-Text-Slider-Rotator-with-jQuery-CSS.html to create a testimonials sliders.

For randomizing your query, just put

'orderby'        => 'rand'

in your $args variable like this:

$args = array( 
'post_type' => 'testimonials', 
'orderby'        => 'rand');

There are way more arguments you can learn from here: https://codex.wordpress.org/Class_Reference/WP_Query

Hope this would help.