Question

I’m using the javascript SDK to fire the send method of fb.ui. It works if I’m logged in as myself and send the messages to other developers on my team. When I log on as a test user and send to another test user, there is no error but the receiver never gets the message.

Code below shows click event from my button:

$(".invite_fb_friends").click(function() {
    <?php 
        $subject = __("Please check out Volved", "volved", "volved");
        if (isset($current_user->volved_cause)) {
            $p = get_post($current_user->volved_cause);
            $invite_id = get_user_personal_invite();

            $description = sprintf(__("Follow this link and join me in supporting %s, or a cause of your choice!"), 
                $p->post_title);
            $link = site_url("/cause/". $p->post_name . "/?invite_id=" . $invite_id);
            $picture = get_bloginfo('template_directory'). '/images/cause_images/' . $p->post_name . '/logo.jpg';
        } else {
            //No cause chosen
            $description = __("If you follow this link, you'll learn about Volved. If you like, sign up and start making a difference."); 
            $link = site_url("/");
            $picture = get_bloginfo('template_directory') . '/images/logo64.png'; 
        }
        //call below documented at: https://developers.facebook.com/docs/reference/dialogs/send/
    ?>

    res = FB.ui({
        method: 'send',
        name: '<?php echo $subject; ?>',
        link: '<?php echo $link; ?>',
        //picture: '<?php echo $picture; ?>', //Does not seem to work with valid URL. HTML shows URL but no pic displayed. Leaving blank shows picture of sender
        //redirect_uri:  filling this in creates an error on facebook
        description: '<?php echo $description; ?>'
    });

});

Answer 1

Test users can only send messages to other test users. If your other user is a real user, your own account for example, it will not send.
From Facebook:
https://developers.facebook.com/docs/test_users/

Limitations

We ensure that test users are exempt from Facebook spam or fake
account detection systems to ensure that you can test your app without
worrying about getting disabled.

Also, to ensure that using test user accounts to test various
scenarios doesn’t end up unintentionally creating spam, we enforce
certain limitations on what test users can do.

Test users can interact with other test users only and not with real
users on site. Test users cannot fan a public Page or create public
content on them like writing on a Page’s wall. A Test user can however
view and interact with the app tab on the Page if they are associated
with that app. They can be accessed and used by any developer of the
associated app. They only have test privileges on the associated app.
This implies that they can use the app in live mode or sandbox mode
but cannot edit any technical settings or access insights for that
app. A test user is always a test user and cannot be converted to a
normal user account.