Revisit our component testing strategy

[vanitabarrett]

What

There are various issues with our tests, coupled together with the fact that we don't currently have any JavaScript unit tests.

There may be some 'quick wins' we can do to give us more confidence. Other things, like adding unit tests, may be dependant (or at least made easier) by revisiting our tooling choices generally.

Why

Our current test setup doesn't give us a lot of confidence when making changes to our JavaScript code. If we're going to be making changes to the way our JavaScript is structured and de-duplicating code, we may want to put better testing in place first so we're more confident about these changes.

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• Tests are reliant on the review app #2565
• Component tests within a test suite are not isolated from each other #2303
• Puppeteer tests can get run against outdated code #2242
• Research best practice - how do other frameworks that use JavaScript approach testing?
• Consider whether there are any benefits to adding end-to-end tests for complex components