there was a lot of comments in PRs that test classes in suppressionxpathfilter should have 2 or more test methods.

This example clearly showed that maintainers tend to forgot this:
https://github.com/checkstyle/checkstyle/pull/7935/files#r399724307

We need Checkstyle to help. There is Check - RegexpSingleline.
Extended doc is at #7714

We need to validate all Classes in suppressionxpathfilter to have 2 or more @Test.
If there are already several of such classes we should be able to exclude such classes from validation temporary with comment "till ".