Depends how you define functionality I guess. If you are talking about high-level user functions (create a new user, modify user, delete user), then lots of org

Depends how you define functionality I guess. If you are talking about high-level user functions (create a new user, modify user, delete user), then lots of organisations probably do have tests for all functions. However, if you consider functions on the code level (e.g. Java methods) then organisations with 100% coverage will be thin on the ground. If you go further and consider line coverage, almost nobody will have 100% coverage. A common problem with organisations claiming to test all functions is that they will only test the happy path - there will be few tests for things like unexpected or illegal input etc.