That's highly dependent on the team, the code, and the tests. For my work, most of the time, comments in the well-structured code are much more likely to still be useful and valid to me and my team over time than a test suite that won't get maintained.

In the past six years, I only worked on one project that justified an extensive test suite. It was a scheduling system for a large machine shop, which allocated multi-step manufacturing tasks across a suite of metal-working machines for dozens of concurrent jobs, while taking into account available machinists, working hours, breaks, vacations, and scheduled maintenance downtimes for each machine. Testing the algorithms for that required setting up a variety of consistent starting conditions, running the scheduler, injecting changes to existing jobs and inserting new jobs at certain times, and making sure that the resulting scheduling decisions were acceptable to the experts who'd been doing the schedules manually and to the machinists.