Add Optimizer smoke test to Site Health integration

[schlessera]

Feature description

If the Optimizer throws a fatal error, it will not take the server down, but rather fail silently and leave the unoptimized output to be sent to the browser.

This means you can have an inactive Optimizer (that just takes up server resources without producing a result) without knowing it.

The Site Health integration should be extended to add a smoke test that tries to optimize a basic page. This way, we can show a warning/error if the Optimizer is fataling. This might for example happen if you have misconfigured it via the configuration filters.

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Acceptance criteria

• The Site Health checks include a basic test of the Optimizer to make sure it does not fatal.

Implementation brief

• Listen to an URL argument amp_site_health_test_optimizer=1
• When the URL argument is present, ensure 'amp_enable_optimizer' is true
• Use hardcoded content to send through the sanitization/validation/optimization pipeline
• Catch exceptions/fatal errors that are happening
• Ensure the end result is optimized AMP
• If not, list the detected errors

QA testing instructions

Demo

Changelog entry