I’m Michael. I was a principal engineer at Facebook from 2009 to 2017, where I was the top code contributor of all time and also conducted hundreds of interviews. I recently co-founded Formation.dev, an engineering fellowship that trains and refers engineers directly into big tech. Ask me Anything!

My view is that both unit tests and end to end tests are important tools for people to work on a large common codebase. 1. Tests aren't only a tool to make sure business critical logic is correct, but they are a tool to make it so someone less familiar with your code can make changes quickly and safely by relying on the tests in place. 2. I believe testing is also a practical matter depending on the application. Tests are not the perfect solution to zero bugs. So you should always be thinking about what are the consequences of bugs in this code, what might happen, would there be unfixable damage done. So you are ready to both write better tests, and respond if things go wrong. That said, I have a reputation for not writing tests, but that doesn't mean I don't think they are important.