And yet, (1) testing finds bugs in any nontrivial program that hasn't been tested, and (2) test long enough and with enough variety and you can make programs significantly more reliable.

Perfect is the enemy of good, and absent academic fantasies of verified software testing is essential (even then, it's still essential, since you are unlikely to have verified every component of your system.)

Sure testing is useful. It's not so useful that you don't need to understand what you're doing though.