# Airbnb reports migrating nearly 3,500 React component test files from Enzyme to React Testing Library in six weeks, against a hand estimate of 1.5 years

Page: https://flyvolo.ai/en/changes/ev-20250314-frontend-developer-1
Date: 2025-03-13 · Stage: Deployment
Can this record move a task judgement? yes
Occupation: https://flyvolo.ai/en/careers/frontend-developer

## Scope

One company's own codebase, published by that company, with the hand-migration estimate (1.5 years of engineering time) supplied by the same company and not checkable from outside. What makes the result reproducible is the mechanism, which the post describes in full: the migration is a state machine whose every step has an automatic referee - jest, eslint and tsc say pass or fail - so the model could retry without a person watching, and the first bulk run cleared 75% of files in four hours. The remaining tail is the more useful number: after four days of tuning, 97%; many of the long-tail files had been retried between 50 and 100 times, and the last 3% were finished by hand. The post is also explicit that the main driver was selecting the right related files to put in the prompt - which grew to 40,000-100,000 tokens pulling in up to 50 files - rather than prompt wording. It reports no change to headcount, hiring or roles, and does not claim one.

## Source

- The Airbnb Tech Blog (Airbnb's own engineering blog) — https://medium.com/airbnb-engineering/accelerating-large-scale-test-migration-with-llms-9565c208023b (primary source)

## What this means

The clearest published account of an LLM migration of frontend code, written by the team that ran it, failures included. Two things generalise. It worked because jest, eslint and tsc each say pass or fail without a person, so the machine could fail and retry overnight: where a frontend task has an automatic referee, expect it to move. And the ceiling: after many of the hardest files had been through fifty to a hundred attempts, three per cent were still unfinished and were done by hand.

## What it does not show yet

A refactor is not new interface work, and a test file has an oracle that a design does not. Nothing here bears on turning a mockup into something that renders, on the states nobody drew, or on what happens on a slow phone — and the post makes no claim about any of that. The 1.5-year hand estimate is Airbnb's own and was never tested against anyone actually doing it by hand, so the headline ratio is a comparison with a number the same company chose. And no role, headcount or hiring change is reported anywhere in it.

## How to verify it yourself

Go through your own backlog and mark each item with what would tell you it is done: a green check in CI, or a person looking at it. The first list is the one that is about to get cheaper, and knowing its size in your own codebase is worth more than any industry figure.


More: https://flyvolo.ai/llms.txt