Commercial CI server now available free

JetBrains, the folks behind many well-loved dev tools (such as IntelliJ IDEA and ReSharper) have announced that TeamCity 3.0, the just-released version of their continuous-integration server, is now available for free for teams of up to 20 developers. TeamCity's stock in trade is ease of use (and particularly good integration with IntelliJ IDEA).

Characterization Tests

In my current column in SD Times, I discuss characterization tests, which are an as-yet little discussed form of testing. They are unit tests whose purpose is not to validate the correctness of code but to capture in tests the behavior of existing code. The idea, first popularized in Michael Feathers' excellent volume Working Effectively with Legacy Code, is that the tests can reveal the scope of any changes you make to a codebase.

You write comprehensive tests of the codebase before you touch a line. Then, you make your changes to the code, and rerun the tests. The failing tests reveal the dependencies on the code you modified. You clean up the failing tests and now they reflect the modified code base. Then, rinse, lather, repeat.

The problem historically with this approach is that writing the tests is a colossal pain, especially on large code bases. Moreover, large changes in the code break so many tests that no one wants to go back and redo 150 tests, say, just to capture the scope of changes. And so frequently, the good idea falls by the way side--with unfortunate effects when it comes time for functionally testing the revised code.To the rescue comes Agitar with a free service called JunitFactory. Get a free license and send them your Java code they will send you back the characterization tests for it. Cool idea. Change your code, run the tests, verify that nothing unexpected broke. And then have JUnitFactory re-create a complete set of characterization tests. How cool is that?

Actually, I use Agitar's service not only for characterization but for my program as I am developing it. The tests always show me unit tests I never thought of writing. Try it out. You'll like it.

How Many Unit Tests Are Enough?

Recently, I was down visiting the folks at Agitar, who make great tools for doing unit testing. Going there always results in interesting conversations because they really live and breathe unit testing and are always finding new wrinkles in how to apply the technique. During one conversation, they casually threw out a metric for unit testing that I'd never heard before. It answers the question of: How many unit tests are enough? You'll note that pretty much all the books and essays on unit testing go to great pains to avoid answering this question, for fear, I presume, that by presenting any number they will discourage developers from writing more. Likewise, if the suggested number is high, they risk discouraging developers who will see the goal as overwhelming and unreachable.

The engineers at Agitar, however, did offer a number (as a side comment to an unrelated point). They said (I'm paraphrasing) that if the amount of test code equals the amount of program code, you're generally in pretty good shape. Their experience shows that parity of the two codebases translates into code coverage of around 70%, which means a well-tested app. Needless to say, they'd probably want to qualify this statement, but as a rule of thumb, I think it's a very practical data point--even if a bit ambitious.

I will see how it works out on my open-source projects. Currently, my ratio of test-code to app-code is (cough, cough) just over 42%. I guess I know what I'll be doing this weekend.