Teamwork

Imagine doing all this locally on your own computer. For simplicity, let's say you've got some code that has to compile and some unit tests that have to run. Easy enough, everybody should be able to do that. Except your manager, who doesn't have the developer software installed at all. Or the intern, who forgot to kick off the unit tests. Or the developer, who works on a different OS making some tests, that aren't important to him, fail (for example, we have an application developed on and for Windows, but a complimentary app for iOS developed on a Mac). Suddenly, getting a working and tested executable becomes a hassle for everyone who isn't working on this project on a daily basis. Besides, the people who can get a working executable may forget to run tests, creating a risk that the executable is compiling, but not actually working. As you can see, a lot can go wrong and there are only two steps. I've intentionally left out all the other tests and quality gates we might have. And that's the biggest benefit to CI. The software is compiled and fully tested automatically, reducing the chance of human errors and making it considerably easier to get a working executable that is more or less guaranteed to work. By testing on a server that closely or completely resembles the production environment, you can further eliminate hard to find bugs.

As you might have guessed, CI is not something you just do. It's a team effort. If you're writing unit tests to make sure everything works as best as it can, but your team members commit large chunks of code, never write tests and ignore the build status, your build becomes untrustworthy and quite useless. In any case, it will not lead to the (increase in) software quality you were hoping for.

Having said all of the above, it's crucial that you, and your team, take your automated build environment very seriously. Keep build times short, so that you get near-instant feedback when a build fails. When someone checks in code that makes the build fail, it should become a top priority to fix the build. Maybe it's that missing semi-colon, maybe a test fails, or maybe more tests have to be added. The bottom line is, when the build fails, it becomes impossible to get an executable with the latest features that's guaranteed to pass your tests and other quality criteria.