Airbnb migrated 3,500 test files with LLMs in 6 weeks instead of 1.5 years

Airbnb used LLMs to move nearly 3,500 React component test files from Enzyme to React Testing Library. The work had been estimated at 1.5 years of manual engineering time and was finished in six weeks.

What they built

An automated migration pipeline that treated every file as a state machine with validation steps (Jest, ESLint, TypeScript). Failing files went through retry loops with dynamic prompts built from the actual errors. Prompts were filled with up to about 100,000 tokens of context: the component's source, sibling tests, imports and good RTL examples. Engineers then improved the prompts step by step from samples of the files that failed.

The result

75% of the files were migrated in four hours and 97% after four days. The whole project took 6 weeks against an estimated 1.5 years by hand. The last 3% were fixed manually, and test intent and code coverage were preserved (self-reported).

Sources