E2E test cache busting on playground.wordpress.net

[adamziel]

Occasionally, people report errors caused by loading outdated versions of Playground assets on playground.wordpress.net. For example, this report:

I ran into an error when I select “Browser” in the storage option:
Fatal error: Uncaught Error: Call to undefined function wp_check_php_mysql_versions() in /wordpress/wp-settings.php:2
One way this could have happened, is if the browser loaded mismatched versions of the WordPress wp.data file and the wp.js file. The wp.js contains a map of where each file starts and ends in wp.data and, given a wrong wp.data input, it would produce the correct directory structure, but each file would have the wrong contents.

Let's solve that.

Done is

1. We start by building a failing E2E test for the following asset types. It should setup the browser and the playground to load a page, then update the asset files, then load the page again in a way that still uses the cached version of some of the assets.
   • php.js and php.wasm
   • wp.js and wp.data
   • service worker
   • web worker
2. We write a patch that makes the test pass
3. We keep the test to prevent regressions

[adamziel]

These related PRs should solve most of the problem described in this issue:

• Service worker: Retry ERR_HTTP2_PROTOCOL_ERROR #949
• Website: Add .htaccess file to prevent caching of index.html and enable importing the client.js library #989
• Use .zip files instead of .data files for loading WordPress #978

The last problematic part I'm aware of is reliable reloading of the service worker, which is tracked here:

#566

We still need the E2E tests to confirm these fixes work reliably.