exclude roles from overview

Yes, the get_users_of_blog() function is deprecated, and the reason your code breaks after using get_users() is the ->user_id part, you should use ->ID instead.

$blogusers = get_users();

if ($blogusers) { 

  foreach ($blogusers as $bloguser) { 

    $args = array( 
      'author'           => $bloguser->ID, 
      'showposts'        => 1,
    ); 

    $my_query = new WP_Query($args); 

    if( $my_query->have_posts() ) { 
      while ($my_query->have_posts()) : $my_query->the_post(); ?>  
        ...........
      <?php endwhile; 
    } 

  } 

} 

If you are on a multisite, you should set the blog_id argument of get_users to your blog’s ID.

Now, about excluding the authors. If you take a look at the author parameters of WP_Query(), there’s a author__not_in argument that accepts an array of author IDs. So, to exclude the test role from your query, set the role__in or role argument of get_users() to test, and then use the results in your WP_Query(). You didn’t provide accurate details so I’m not sure what exactly you are looking after, but these should do the trick.