As Kent Beck advises, "Write tests until fear is transformed into boredom," and anyone who has been witness to a production deployment issue is all too aware of this fear. Tests can help us gain confidence in the code we are about to write and in the CI/CD environments we have set up so that the act of pushing new changes can be stressless and perhaps even fun.

There are several tools we can use for testing applications, and various levels at which to test. When is it time to write a new test? Should that new test be a unit test or an integration test? Just what is the difference between unit and integration? Is end-to-end testing a worthy investment? And how do I get started?

I will answer these questions and more based on my experience and opinions as a full-stack software engineer who has written tests at every level. I will also demonstrate how I helped take an application with low test coverage and began introducing new tests using libraries like Playwright and React Testing Library, and adding them in our GitHub Actions workflows.