Halo2,
Backend-infra encourages you to start writing test in this Q4 2017. Writing test takes a lot of time at first, and you should start training yourself to do it. It's a huge investment for our (ironically) development velocity and of course service reliability. We target to enable TDD and CI/CD by Q1/Q2 2018, and it's impossible with our current testing culture and test coverage.
You're not alone! We're doing it as well. Backend-infra are improving our codebase test coverage and we'll tell you our stories in Testing Stories blog post. This is our first post, improving ffx-core library test coverage. We're trying to post it regularly so you'll know our progress, difficulties, and practices.
So let's start writing test! Save your on-call time to train your testing skill, you can test anything, read this page first, and if you have any problem just ask our team!
Last but not least :
Stop writing legacy code.