Weir documentation tells how to write tests but not how to run them

Maybe I'm missing something. I've been reading through `https://writewithharper.com/docs/weir` and `https://writewithharper.com/docs/contributors/testing-strategy` and I can find the docs for how to add `test` and `allows` testing lines to a Weir linter, but I can't find how to run the tests.

Normally I do `cargo test` but that tests everything. I know there are shortcuts but as I seldom use them I don't remember them. I also know that I was given some advice on how to test them in the Discord, but I've forgotten those too.

Best to add them to the docs.

Start with the Weir documentation and the contributors’ testing-strategy page linked in the issue, then check the repository’s existing test commands to confirm the relevant targeted workflow. Done means the documentation explains how to run Weir linter tests without running the entire suite, alongside the existing instructions for writing test and allows lines.

Written by the indexing model from the issue text.