Better testing infrastructure

[Keavon]

We have, so far, written a minimal amount of tests in order to focus on rapid prototyping without major concern for breakage, in the absence of actual users. As the scope of the project grows, the permutations of cases where regressions can crop up is making it harder to detect bugs purely by hand. Users might also care about stability, even though 0.1 is alpha.

We should build testing infrastructure to help create tests. Thanks to the project architecture which is split between the Editor Frontend, Editor Backend, Graphene, and (eventually) Charcoal, with the message dispatch system tying them together, it should be pretty easy to write tests in general by writing many tests using messages. Some infrastructure can include a way of recording messages for easy copy and paste into tests, thereby turning manual tests into automated tests.

This issue can serve as a good place to discuss other forms of testing infrastructure to help make it easy to write and maintain efficacious tests.

[bjorn3]

https://matklad.github.io/2021/05/31/how-to-test.html is potentially relevant.