Edit your test post to run a plugin. Find the Shortcode block under Widgets.
Go to the Plugin Editor. We’re going to cannibalize the Hello Dolly plugin that comes as default with every installation.
* The reference to “a new version of My Table” is actually a reference to Hello Dolly, somehow remembered by core. If you click “update now”, all the code for the Hello Dolly plugin will revert back.
** Note: It is possible to modify and update the plugin code while it is active, and still get the shortcode in the post to display as you’d expect. But, sometimes you’ll get an error. If that happens, open another window, deactivate the plugin, then go back and update the code.