Regression

A regression is when a change breaks something that used to work. You add a new feature or fix a bug, and a previously fine part of your product silently stops behaving correctly. Regressions are insidious because the broken thing often looks unrelated to what you changed, so they slip past you and get noticed by a customer instead. For a lean founder moving fast, especially with AI writing code, regressions are the main hidden cost of speed. The defence is regression testing: an automated suite that re-checks old behaviour every time you change something, so a break trips a red light before it reaches production. You do not need full coverage on day one; you need tests around the paths that matter most, money, login, core workflows, so the features customers rely on cannot quietly rot while you build new ones.