Your Tests Passed. So Why Is Your UI Broken?
So your team just pushed a CSS update. All your functional tests pass, the deployment goes through, and everything looks fine in-browser. Two hours later, a user reports that the checkout button has disappeared on mobile. Technically, the button still works, but now it’s hidden just below the fold, so your tests had no way to flag the issue. This is what’s known as a visual regression, or visual bug, and it’s one of the most common ways UI problems slip into production unnoticed.