3 Comments Test types and Continous Integration - 02/23/09
Martin Fowler defines continuous integration as follows:
“Continuous Integration is a software development practice where members of a team integrate their work frequently, usually each person integrates at least daily – leading to multiple integrations per day. Each integration is verified by an automated build (including test) to detect integration errors as quickly as possible. Many teams find that this approach leads to significantly reduced integration problems and allows a team to develop cohesive software more rapidly.”
I’m writing this post as a follow-up to my previous one, types of testing. I’ll talk about how each type of test, fits into a continuous integration process.
You can read all about Continuous integration in Martin Fowler’s paper here. A nice addition (and one that’s lying on my bookshelf as many others), is the book -> Continuous integration: Improving software quality and reducing risk, by Paul Duvall, Steve Matyas and Andrew Glover.
I’ll be talking about two types of builds. I’ll refer to them as the commit build and the secondary build. The primary-stage build (aka the commit build) automatically runs whenever someone commits changes to the repository (see Every build should build the mainline on an integration machine). When this build has tests that fail, the build also fails. The broken tests must be repaired as soon as possible to fix the build. This is a show-stopper and must be dealt with as soon as possible. The secondary-stage build, is a build that runs whenever possible; in my opinion, at least once a day. It can be done manually, or it can run as a nightly build in a script that grabs the latests executables and runs these specific test suite. If this build fails, developers can carry on working. Don’t get me wrong, this build has to be fixed too, but it doesn’t have the same priority as a broken commit build.
Unit tests are the most important part of your continuous integration process (in the sense that these tests are ran the most). After each commit to the repository, the build executes all unit tests to finalize the commit. Your unit tests should run within the commit build and make the build fail if any test fails.
It’s very important to keep these tests focused, and especially fast. You must realize that each commit will execute the tests, and it’s important to have immediate feedback. You can’t be waiting half an hour just to commit some changes, right?! That’s why unit tests use test double patterns (use a test double for each of the SUT’s expensive dependencies). I’ve only read a few pages in Meszaros’ book, but I know it contains a chapter that covers these patterns (can’t wait to get there!).
Integration tests run within the secondary build. These tests are normally slower than unit tests since they test the integration of several components, thus they do use (and set up) actual dependencies. This makes these tests slower, but still, we should try to keep them relatively fast. Running these tests is also very important, but since it’s an expensive operation, we do it far fewer times than running the unit tests. In my opinion, they should run at least once a day. These tests normally include testing access to your database, so I try to run these tests after each database-change, for example. If they fail, you’ve probably broken a NHibernate mapping, a typed DataSet, or some code using an ugly magic string somewhere. My rule is, run them at least once a day, and every time you’ve made a change that directly affects the integration of your code with an external component.
If you’re using automated acceptance testing, these tests should can also be executed automatically within your integration process. I think it’s a good habit to run these tests daily, only it can be very annoying when developing your user interface. Whenever you need to add some textbox somewhere, you’ll have some failing tests (hopefully -remember TDD-). In that case, I tend to keep the general rule of having them all pass at the end of the iteration, that’s the final deadline. If you choose to do so, it might be a good idea to set up a third build, or to just run them manually as part of your iteration (a bit like regression tests in this sense). If you just run them at the same level as your integration tests, you’ll have your secondary build failing during the whole iteration, which is not a good thing.
If you’re doing user acceptance testing, you should have your CI process deploy your application to the UAT-environment automatically (we do this after each iteration).
I’ve heard of projects where the secondary build also includes performance tests. Usually I don’t think this is necessary, unless in applications where performance is absolutely critical. If a certain level of performance is a requirement, including them in your continuous integration process gives you the advantage of constant feedback and easily identifying what part of your code might contain a memory leak and needs some investigation or rolling back.
I’d use these rules to make up my mind:
1) Do I really need performance tests?
2) Do I really need constant feedback on my application’s performance?
3) Can I have these tests executed by an independent build (not in the commit build, nor in the secondary build)?
Smoke testing and regression testing
I have skipped these two types of tests out of my initial list in my previous post, because these are just unit tests, integration tests, acceptance tests or performance tests in the long run. The big difference in the naming is just because of when they are executed, basicly. And in a continuous integration process, this would be during the commit build, or during the secondary build (or any other builds), depending on the type of test .
I think this post gives a nice overview of what tests to put in what build within a continuous integration process. Maybe this approach isn’t the best one, so if you’ve got any other ideas, be sure to leave them in the comments .