Exploration Through Example

Example-driven development, Agile testing, context-driven testing, Agile programming, Ruby, and other things of interest to Brian Marick
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Thu, 08 May 2003

Learning tests

Mike Clark writes about learning tests. They're tests he writes to figure out an API. He's made me think about one of my habits.

I tend to use the interpreter for learning. Where Mike describes writing a test to see what the return value of a method is, I would do this:

irb(main):001:0> load 'timeclock-web-services.rb'

irb(main):002:0> session = start_session
@active_job_manager=<ActiveJobManager: {}>, @records=[],

irb(main):003:0> puts session.methods

What does this gain?

  • It's faster than going through a testing cycle. I suspect I ask more questions than I otherwise would, because asking a question is so easy. I'm more apt to explore rather than stick to just what I think I need to know.

  • The interpreter tends to spew out a bunch of info at once. The several lines above show the contents of an ActiveJobManager within a Session within a RichlyCalledWrapper within a RichlyCallingWrapper. So a single question tells me a lot about what's going on, even though the spew is roughly as obfuscated as XML. In contrast, in a test, I get only the answer to the question I think to ask.

What does it lose? (Leaving aside that you can't do it in Java.)

  • You lose the tests and the documentation they provide. (I've never been quite comfortable with tests as documentation - I'd rather go to the code - so I think I underplay that testing role.)

  • Mike mentions extracting code for dealing with the API from the tests. I do some of that, since I will often write a little file of utilities that I load to help me explore. But they don't tend to get preserved and reused.

  • Having a file full of tests probably encourages methodical exploration, whereas an interpreter transcript makes it easier to overlook things. (This is the flip side of the last of the advantages.)

I've done roughly what Mike does, but only (I think) when I'm trying to learn a package preparatory to changing it. That's a different dynamic. I'm acting mostly as a maintainer who wants a safety net of tests, not just as a user of the API. So I think I'll adopt Mike's style next time I want to understand an API. Since Mike's doing some Ruby, maybe he'll try my style. I bet there's a blend that's better than either: a way of rapidly cycling between typing at the interpreter and typing tests in a file.

## Posted at 15:35 in category /testing [permalink] [top]

About Brian Marick
I consult mainly on Agile software development, with a special focus on how testing fits in.

Contact me here: marick@exampler.com.




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