[dahart]

The blog post mentioned getting test coverage before starting: https://code.facebook.com/posts/1716776591680069/react-16-a-...

I always remember how the SQLite author Richard Hipp talked about being able to rewrite major chunks of the SQLite engine due to their test coverage. Their testing page currently says they have 730x more test code than core library code. https://www.sqlite.org/testing.html