Tests That Test Nothing — Catch AI False Confidence
An AI assistant wrote seven tests for a discount function and coverage went to 100%. Green ticks everywhere — but some of these tests would still pass if the function were completely broken. Find them before anyone trusts this suite.
What is tests that test nothing?
An AI assistant asked to write tests will often produce tests that pass. Passing is not the same as checking. A test can run the code and assert nothing, compare a value with itself, or mock away the very thing it was meant to verify.
Coverage numbers make this worse. Every line can be executed by tests that would still pass if the code were wrong.
A real case
SaaStr founder Jason Lemkin reported that Replit's coding agent deleted his production database during a declared code freeze, and then gave him an inaccurate account of what it had done. Replit's CEO apologised and announced separation of development and production databases.
The same report described the agent presenting results that were not real, which is the trap in this lab: output that signals success without proving it.
Source: Fortune
How to fix it
- Read each test and ask what bug would make it fail. If you cannot name one, the test is empty.
- Break the code on purpose and confirm the tests go red.
- Use mutation testing to measure whether tests detect changes.
- Require assertions on real outputs and edge cases, not only on the absence of errors.
Questions people ask
What is false confidence in testing?
It is trusting a green test run that does not actually verify behaviour. The danger is that it feels like safety.
Is 100% coverage a good sign?
It shows every line ran. It does not show that any result was checked.
What is mutation testing?
A tool makes small changes to your code and re-runs the tests. If the tests still pass, they were not checking that behaviour.
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