Add send message buffering

Set up

1. Open message/externallib.php
2. Find the send_messages_to_conversation function
3. Add a sleep(2); into the function to make it take longer to respond to the client

Spam from desktop

1. Log in as admin
2. Open the message drawer and go to the message settings
3. Enable the "Use enter to send" setting
4. View the admin self conversation in the "Starred" section
5. Send a few messages as fast as you can (you can just hit enter to send them)
   • I would suggest you use ordered numbers for the messages to make it easier to confirm the order is correct, e.g. 1, then 2, then 3, etc...
6. CONFIRM that each message is added to the page as soon as you send it
7. CONFIRM that the message has a loading spinner up the top right while it's being sent to the server
8. CONFIRM that you can immediately send the next message even while the first one is loading
9. CONFIRM that when the message is saved on the server the loading spinner is replaced by a time
10. CONFIRM that the messages are rendered in the UI in the order that they were sent

Spam from mobile

1. View your site from a mobile (from an actual mobile, not in "responsive design" mode in the browser)
2. Log in as admin
3. Open the message drawer
4. View the admin self conversation in the "Starred" section
5. Type in a message and send it by pressing the Return/Enter key on the mobile keyboard (not by clicking on the send icon in the messaging interface)
6. While that messaging is sending keep pressing the Return/Enter key on the keyboard to try to spam the same message
7. CONFIRM that you can't spam the same message. It is only added once. The text area should be cleared as soon as the message is first sent.
8. Try sending a few more messages
9. CONFIRM that you can keep sending messages while each of the previous messages are being sent (same confirmations as in the "Spam from desktop" test)

Error sending message

1. For this test to can revert the changes you made to message/externallib.php
2. Log in as admin on a desktop browser
3. Duplicate the page in another tab so that you've got 2 tabs open with the Moodle site
4. In the first tab open the message drawer and view the self conversation
5. In the other tab go to site administration > messaging > messaging settings
6. Disable site messaging by unchecking the "Enable messaging system" checkbox and saving the changes
   • This is going to cause our messages to fail to send
7. In the first tab try to send a message
8. CONFIRM that the message fails to send. It should have a red border and it should have a "Retry" link instead of the time at the top right.
9. Click the retry link
10. CONFRM it still fails to send
11. In the other tab enable the site wide messaging again
12. In the first tab, click the retry link again to try to resend the message
13. CONFIRM that the message successfully sends. The red border should be gone and the "Retry" link should be changed to the message time.