I used to think Unit Tests was useless. Then I broke prod

I used to think unit tests were useless, and then I broke prod at work. It was also extremely dumb thing like, had I literally did two test cases, it would have worked. Just like two more unit test cases. It was about a right regular expression validator. What was happening in the code base, there's, um, code base, there's, um, that we have a form that we have to send and there's a validator. The app uses, like a regular expression in order to check if something is right or not to send, like a package. So I was like, okay, fine, let's just allow front and the back. Spaces. Little did I spaces. Little did I didn't check in the middle. What it literally blocked any spaces that people wanted. Packages with spaces, names with spaces. This would have been caught by QA. A. Team at we didn't have any automation tests. He didn't know how to test this. And I'm pretty sure he accidentally took this version into prod. Cause at the time, we didn't have like, differentiate release from snapshot. And it was a huge ruckus to try and get the version back.