It's too difficult for npm contributors to figure out what the conventional style is for tests. Part of the problem is that the documentation in CONTRIBUTING.md is inadequate, but another important factor is that the tests themselves are written in a variety of styles. One of the most notable examples of this is the fact that many tests use fixture directories to store precooked test scenarios and package.json files. This had some negative consequences: * tests weren't idempotent * subtle dependencies between tests existed * new tests get written in this deprecated style because it's not obvious that the style is out of favor * it's hard to figure out why a lot of those directories existed, because they served a variety of purposes, so it was difficult to tell when it was safe to remove them All in all, the fixture directories were a major source of technical debt, and cleaning them up, while time-consuming, makes the whole test suite much more approachable, and makes it more likely that new tests written by outside contributors will follow a conventional style. To support that, all of the tests touched by this changed were cleaned up to pass the `standard` style checker.
Some fixtures are necessary, but they should all be combined into one place to signpost what they're for. Part of #7929.