Continuous Integration

Continuous Integration, or CI, is the practice of automating the running of tests when new code is submitted to a central repository. Whereas, when originally introduced back in 1991, it could be understood as running a "nightly build", as running the tests took time and was expensive, these days, it is commonly understood as running a set of tests with each new code submission.

The objective is to produce code that always works. After all, if it's not, it is detected quickly by the failing tests. This fast feedback loop helps developers to increase their speed and create a safety net that allows them to focus on whatever feature they are implementing and leave it to the CI system to run the totality of tests. The discipline of running the tests automatically and on every single test greatly helps to ensure high-quality code, as any error is detected quickly.

This is also dependent on the quality of the tests that are run, so in order...