TestGen-LLM
Meta's TestGen-LLM uses LLMs to improve existing human-written tests - augmenting coverage rather than generating tests from scratch - while rigorously filtering LLM output for quality.
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Assured offline evaluation: Every LLM-generated test must compile, run, pass deterministically, and improve coverage of an existing test class before it is presented to engineers - hallucination is filtered out up front.
Deployed at Meta: Rolled out during Instagram Reels and Stories test-a-thons, then extended across Instagram and Facebook codebases.
Success funnel: 75% of generated test cases build correctly, 57% pass reliably, and 25% increase coverage of existing classes.
Engineer uptake: Software engineers accepted 73% of TestGen-LLM's recommendations for production, improving 11.5% of the targeted classes.