Implement Testing

[jtfairbank]

I think it's a good idea to implement testing given the fact that I broke production a few times recently, and that we have a bunch of new contributors. Does anyone have any thoughts on how to best approach this for a Gatsby / React site? I'd like to keep it simple enough that our new contributors can pick it up fairly easily.

@coderbyheart I know you do some really cool testing-in-prod stuff! Would that be relevant here?

[raae]

I had success with the docs on testing last time I set up testing for a Gatsby site.

[coderbyheart]

Because this is a content heavy website and there is little logic to test (which also has some complicated dependencies to set up), I'd also recommend to use an end-to-end testing framework, as @raae already did

Playwright is very easy to get started, very fast, designed for SPA (which Gatsby is not, but our website has content that is displayed using Client-Side JavaScript) and I have working examples for GitHub actions.

[coderbyheart]

Since I had previous work, I've added a demonstration in #589