Monday, February 9, 2009

Test Data Builders

I've been meaning to post something about this for a little bit, not exactly sure what I had to add to the subject besides, "hey that's a good idea", and after about a month thinking about it I think it's safe to say I don't have much to add except for evangelism.

So without further ado, I'd suggest reading a few articles on test data builders:
Test Data Builders

In short Test Data Builders allow you to minimize maintenance cost in your tests and allow you to easily inject objects into your test objects, it's great, great stuff.

I guess I do have an addition, a story:
On my last project a co-worker made a perfectly reasonable api change, and added a parameter to a constructor, after making the change he realized this would effect ~100 tests (whoa), so he used Eclipses magic refactoring tools and initialized the value to null. The problem was his changes really required that new parameter to be non-null (in fact if it was null a NPE would be thrown), and even though the code compiled all the tests broke (with NPEs). He didn't want to fix the tests. Why should he fix all 100 unrelated tests, maybe 5-10 tests but 100, that was just too much. And really I understood that. And I was lucky, I had just read Jay Fields post about Test Data Builders. 1/2 a day later a co-worker and I added all the Builders we needed for our project and started updating our tests to use those builders. With the builders in place, fixing the NPEs was in one place. And now, if there is a similar situation and one change breaks hundreds of tests, there is one place to go and fix them all.

Anyway, I would not start a new project without using Test Data Builders they really pay for themselves when maintaining your tests and your code.

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