Update __fixtures__ (maybe?)

[thedavidprice]

@dac09 @peterp
Admittedly, I don't pay a lot of attention to the two __fixtures__ directories in the monorepo. But when I looked through them today, I noticed they're not up to date with latest features/syntax.

I'm guessing it's not ideal, but is it ok? (For now?)

PP, I know there's a pending project to re-write/structure testing, which would include fixtures. My questions here are mostly concerned with whether or not we could be relying on faulty tests between now and then. Again, I'm assuming we're ok and have been updating the parts we are using for tests. (Right? 😬)

[thedavidprice]

@jtoar I have an intermediate step here. This would be a part of a testing overhaul, that won't come until after v1. But in the meantime I have an idea to try along with needing to consolidate the open Issues related to overhauling testing and CI.

[jtoar]

The first step will happen in #3914.