You’re making the mistake of thinking that if it doesn’t work perfectly then it’s useless. In very large systems, that’s not the case. Even if testing only worked in half the cases where it could be used, it will still make an impact on the average number of people infected by each newly infected person. We need to take a lot of different measures all at the same time, in order to beat this: masks, social distancing, contact tracing, testing those who may have been exposed, and isolating those who test positive.
Saying “there’s little point in testing” isn’t just wrong, it’s dangerous, because somebody might believe you.