Mutation Testing: Why Code Coverage Isn't Enough

Mutation Testing: Why Code Coverage Isn't Enough

How the Stryker tool reveals the true strength of your test suite — using a real business rule with clear limits.

A green "100% code coverage" badge feels great. But here's the uncomfortable question QA should ask: coverage says a line ran — does it say the behaviour was verified? If someone changed that line, would your tests notice?

Mutation testing answers exactly that. In this article I show it with Stryker + Jest, applied to a grain-service-fee business rule (a nod to agribusiness domain rules).

Full, runnable source on my GitHub.