Wikimedia Bugzilla is closed!

1) Add to [[Wikipedia:Sandbox]] the following code (e.g.: https://en.wikipedia.org/?oldid=481562172):
<div id="foo-bar" style="display:none;">
{| class="wikitable mw-collapsible mw-collapsed"
|-
!A||B
|-
|C||D
|}
</div>

2) Add to [[Special:MyPage/common.js]] the script below (e.g.: https://en.wikipedia.org/?oldid=481560711)
$( mw.util.addPortletLink( 'p-namespaces', '#', 'Test now!' ) ).click( function ( e ) {
   $('#foo-bar').show();
} );

3) Open the sandbox and click on "Test now!"
4) It will appear a table like this:
+----------------+
| A | B [expand] |
+----------------+
| C | D          |
+----------------+

5) Click on "[expand]" and the same table will be displayed, but now with the "[collapse]" button:
+------------------+
| A | B [collapse] |
+------------------+
| C | D            |
+------------------+

6) Click on "[collapse]" and it will appear a collapsed table like this:
+----------------+
| A | B [expand] |
+----------------+

As you can see, although we added the class "mw-collapsed" and the button in the table from (4) says "expand", the table is not collapsed!