When running tests, it's a great feeling to see dozens of green check marks indicating that a test suite is passing. It's especially gratify

Avoiding False Positives in Node.js Tests

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2024-11-20 12:30:02

When running tests, it's a great feeling to see dozens of green check marks indicating that a test suite is passing. It's especially gratifying after tackling a tricky bug or slogging through a tough feature. But those passing tests may be giving you a false sense of security.

Often, bugs lurk in passing tests, undermining trust in the test suite and your application. Such tests can cause more harm than good, giving you a hearty pat on the back while hiding broken functionality. It can take months to weed out a false positive test, and that might be only after a customer complaint.

This post examines several common false positive patterns that can crop up in test suites. Taken out of context, the examples may appear obvious, but they find their way into complex, real-world tests all the same.

Although I don't intend to be technology-specific, inevitably some of the pitfalls are specific to quirks in the JavaScript ecosystem (particularly its UI testing libraries). I expect readers will be unfamiliar with some (or most) of the libraries featured in the post, but I hope the underlying principles will be relevant.