The thing is that tests are code, and all code is technical debt, but unlike normal code tests can grow without bounds, and they don't always get seen as a something with a cost because they don't get shipped to production.
-- https://www.brandons.me/blog/thoughts-on-testing
i use tests sparingly. for complicated, algorithmic tasks i use test driven design, but otherwise, i usually stopped striving for a high coverage. too many of the tests i see are badly written and more of a liability rather than providing value; they exist to satify code coverage requirements.