Tests waste a lot of time. That's certainly true for some teams. On the other hand, those tests have saved me in case a useful documentation is lacking which is

Tests waste a lot of time. That's certainly true for some teams. On the other hand, those tests have saved me in case a useful documentation is lacking which is virtually true for almost every closed source software project. To be fair, sometimes these tests were also misguided by misunderstood requirements, providing a false "documentation".