[LoSboccacc]

"The outlook for the effectiveness of testing used by itself is bleak. Jones points out that a combination of unit testing, functional testing, and system testing often results in a cumulative defect detection of less than 60 percent, which is usually inadequate for production software."

https://medium.com/@TuckerConnelly/94-gems-from-code-complet...

personally I like write some cursory unit test because it ensures the code logic is correctly decoupled from data retrieval, but most of my unit tests are written from user reports, as part of a large no regression suite.