Your Go Tests Pass, But Do They Actually Test Anything? An Introduction to Mutation Testing

GitHub Copilot, Cursor, Claude Code — these tools can generate hundreds of lines of Go in seconds. But there's a problem that doesn't get enough attention: AI-generated code ships with AI-generated confidence, not correctness. Your test suite says "all green." Your coverage report says 85%. But how many of those tests actually catch real bugs? How many are just going through the motions — executing code paths without verifying behavior? This is where mutation testing comes in. And this is why I built mutest. The Hidden Cost of AI-Assisted Development AI coding assistants are good at producing code that looks correct. They generate functions with proper signatures, idiomatic error handling, and even test files. But there's a gap: AI tends to produce tests that cover code paths rather than verify boundaries. Consider this function: func IsEligibleForDiscount(quantity int) bool { if quantity >= 10 { return true } return false } An AI might generate tests like: func TestIsEligibleForDis