Targeting Quality 2019

If you take comfort in knowing that your unit test suite has very high coverage, or think that increasing your test coverage will guarantee catching bugs earlier, I have some bad news. Your test coverage metrics are lying to you.

If you’ve already been bitten by bugs that turned up in code that you thought was thoroughly tested, or suspect that your unit tests leave something to be desired, I can provide some hope. There is a better way!

In this interactive demonstration, I will use just a few lines of Javascript to achieve 100% test coverage without actually testing anything, and then show how using mutation testing tools can expose those lies without writing a single new test.

If you rely on unit tests in your development process at all, you’ll see how this simple technique can be used to evaluate your actual test coverage and highlight exactly what kinds of bugs you might still be missing.