Function not receiving string from shortcode

It appears like you can not use upper case like that in a shortcode. Instead of videoUrl, use video-url:

function get_youtube_thumb_url_func( $atts ) {
    $atts = shortcode_atts(
        array(
            'video-url' => 'urlHere',
        ), $atts, 'youtube-thumb-url' );

    return $atts['video-url'];
}
add_shortcode( 'youtube-thumb-url', 'get_youtube_thumb_url_func' );

And your shortcode:

[youtube-thumb-url video-url=”test”]

This is the final function that I tested before posting.