Facebook Engineering


JiTTests (Just-in-Time Tests) are LLM-generated tests created automatically when code changes are submitted, designed to catch regressions without manual maintenance. Unlike traditional static test suites that require ongoing updates and review, JiTTests infer code change intent, simulate potential faults through mutation testing, and focus on true positives using ensemble assessors. This approach eliminates test maintenance costs, adapts automatically to code changes, and only requires human review when actual bugs are found, addressing the strain that agentic development places on traditional testing paradigms.

The Death of Traditional Testing: Agentic Development Broke a 50-Year-Old Field, JiTTesting Can Revive It