Extreme Programming: Continuous Integration

red-green-refactor-commitAs professional developers, we want to get feedback as soon as possible in order to detect any potential issues in our software. To do so we can practice Test Driven Development (TDD) to make sure that our code is fully tested. We also have a full acceptance tests suit that prevent us to have any regression regarding existing features.

Yet this might not be enough to ensure the quality of the software we build. It is likely that you work in a team with more than one pair of programmers.

Conflicts and merges

Now imagine that two pairs work on different user stories, each duo practice TDD to ensure the quality of their developments. After a day or two both teams are done, all tests are green and the acceptance tests still passed, time to commit/check-in the code to the source control.

But unfortunately both pairs updated a common part of the project, the first team will commit their changes without any issue. But the second team will have to deal with a lot of conflicts and merges before being able to save their work on the source control.

Maybe you haven’t experienced situations like this one before but if you do, you probably know the pain it can be to merge a project full of conflicts, it can take hours…

Avoid Big-Bang commit

Conflicts and manual merges occurred, there is always a time when several developers work on the same part of a project. But it is possible to ease this process in order to avoid such situation.

You need to integrate your changes often, do not wait the end of the day to commit your code. It is preferable if the commits occurred every few hours or even sooner. This way the conflicts you might have will be way easier to solve.

Whenever you want to integrate your code to the source control you have to make sure you have the latest version on your machine in order to check if all tests (acceptance ones included) pass otherwise you need to fix them before proceeding to the commit.

With modern tools at our disposal it is possible to automate the continuous integration process. You commit your changes, then the source control build the application and run all tests. If it is green, the project is deployed (most likely on a development environment) otherwise the code changes are refused and you need to fix the issues before trying again.

Extreme Programming is mainly focused on getting quick feedbacks, with unit tests for the code, acceptance tests for the business requirements. Continuous integration has the same goal of shortening this feedback loop, this practice helps a team to avoid Big-Bang commits with massive breaking changes that lead to compatibility problems, huge conflicts and painful merges sessions.

See you next time!

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