Freitag, 11. Dezember 2009

Dieser Blog ist tot. Ich blogge weiter auf dem «Agile Trail».

Running only one of JUnit's Tests

Green Bar with only one of JUnit's Tests

I managed to run all of JUnit's tests. And I failed for some time to run only one test. Here's why and how I finally succeeded.

One test I kept a close eye on: org.junit.tests.running.classes.ParameterizedTestTest. I opened it in Eclipse and tried to run it. A window occured and asked me to select a test:

What was that? I never saw such a window before. Was it something new in Eclipse 3.5.1? I looked around and looked also into the outline of that test class:

After a closer look I thought I knew what that test selection window was all about: One was able to pick a specific test method in one test class. All of the test method names in the test selection window were also in the outline view of that class. Yes, that would make sense. And that would be actually a great thing, since it was never possibile to do that in previous Eclipse versions and that would be a very useful feature for many reasons.

Okay, new feature, cool. But how could I run one test class with all test methods together? Like I was used to do in all the previous Eclipse versions before? I asked other Eclipse users in my current project, but nobody had a clue. I asked on Twitter, and got some doubtful suggestions like "I think there is something seriously broken in your eclipse installation."

After the fifth person or so I begged for help I realized what was going on. Do you see it? It's in the pictures I showed you in this post before. What I saw after a while was this line:

What a bad UI design, I thought. Why on earth would they put an entry for the whole test class in the middle of all the other test methods? Shouldn't it at least be marked in some way? Wrong assumption, again. Those items were all test classes! Oh my, now that I look at the test selection window I see all those green icons with the C in it...

Anyhow, why are there so many static test classes (yes, that's what they are, static, and the outline view told me with a little red 'S') in one single file? Because those are the input parameters for the tests. The test class contains all the tests for JUnit's Parameterized Test feature, which is a way to deal with one test method called several times with different parameters. It's more than having a for-loop going through a bunch of parameter sets, because with JUnit's Parameterized Test feature every parameter set is treated like a separate test method. With three parameter sets you'd end up with three tests, and if one test would fail, the others won't stop running like they would do in a for-loop.

For that feature you have to provide a annotated method which should return the parameters, you have to provide a constructor and instance variables for the parameters, and you have to reference the parameters in the instance variables from within the test method. That's a lot of stuff which could be broken easily. Each static test class supports a test method for the feature. Eclipse cannot distinguish between a test class as a test class and a test class as a test input parameter, and so it showed every test class in a test selection window.

Well, maybe I shouldn't program late at night, but that was really a hard one to figure out.

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