At Google, because everything is in the mono repo and nearly everything around it is in some level of flux, if you don’t have a test for your code, it gets broken pretty regularly.

Most teams are pretty understanding when they break you on some untested code, and will work with you to fix it, but the very first step in working together is for you to write a test that shows the issue.

The resultant culture is heavily biased toward writing tests before something bad happens to you.