buildifier rule with check mode is deprecated but buildifier_test is not documented

In the documentation only buildifier rule is explained
https://github.com/bazelbuild/buildtools/blob/master/buildifier/README.md#setup-and-usage-via-bazel-not-supported-on-windows

There is also no test in the buildtools repository that uses buildifier_test rule in order to check how it is to be used.

The only option is to dig in the implementation or into some PR / issue comments.

Start with the README.md section on setup and usage via Bazel, then inspect the buildifier_test rule implementation and the referenced PR or issue comments to establish its intended use. Add documentation for the rule and a buildtools repository test demonstrating that usage; done means a newcomer can follow the documented setup without reading implementation details.

Written by the indexing model from the issue text.