The importance of integration testing

I’ve been studying integration testing quite close for the past year, especially since being a contributor to the JBoss Arquillian and ShrinkWrap projects, which target automated enterprise integration testing. This is a part which is almost non-existent in the enterprise today. Sure, if you have > 95% code coverage by unit tests you can be pretty certain that the business logic behaves like it is supposed to. But you are still testing your code in the wrong context. You still need to test your code in your target environment, e.g. how does the code actually behave when run in your application server, with a specific Java version, etc?

Unit tests are great and should be the cornerstone for each application that is developed today. But unit tests alone are not enough. You also need to test your code in the proper context, in the context where it is going to live in for a far longer time than it took to implement and release the first version. You need to test your code in the same environment that is going to be used in production. Why? Imagine a Formula 1 team creating a new aerodynamic part. If their simulations return promising results, they evaluate the part in the wind tunnel. But if the wind tunnel tests turn out good, they don’t put the part onto their race car five minutes before the start of the next race. It sounds like a silly thing to do, but that is exactly what is going on in system development today! The Formula 1 teams test new parts on the test track for days, in the right context – with wind, humidity, heat, stress, endurance, etc. Every parameter playing its part for the new detail that is being tested. Then they carefully analyze the results, before they decide whether this new component fits into the production environment (which is on the car during a Grand Prix weekend).

It’s when we connect pieces together, cogwheels to moving parts, when it gets interesting. How are the pieces working together? Do the cogwheels fit together at all? Is there friction which causes overheating? Can the pieces survive high torque? This is something that is extremely important also in software development, but is often neglected. I’ve been in projects where large teams works in two, three or four week sprints, but at the end of the sprint when all new code is integrated, the artifact doesn’t even deploy! It then usually takes a couple of developers two days just to integrate the code to make it deployable. And when it finally deploys, it doesn’t say anything about if the code works or not. A deployment is just like turning the key when starting a car. Only because the engine starts, it doesn’t guarantee that you can actually drive it. Integration tests should be a part of the continuous feedback cycle. As soon as a part doesn’t fit with its surroundings, you should be notified as soon as possible, not four weeks later.

Integration testing is a broad topic and there are different types of integration tests, which needs be handled differently when incorporated in a deployment pipeline. But that’s a subject for a later blog post. All in all, integration tests are important. If you wan’t to have a streamlined development process, where getting new features into production fast without sacrificing quality, you’ll need to have proper integration testing in place.

Tommy Tynjä
@tommysdk