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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Sun, 30 Oct 2005

Welcome, Better Software readers

In my editorial for the November Better Software, I use the string of numbers at the top of my blog as an example of a big visible chart. They've helped me lose about 25 pounds. Especially once I started meeting people who told me they tracked them, my impulse to show the world steady progress remained strong for about 20 of those 25 pounds. (I've even met someone who said he was inspired to do the same with his blog.)

More recently, progress has been more fitful, as can be seen by the abundance of red. (Green means I've lost at least two pounds in the week, red means I've lost some but not enough, and bolded red means I've gained weight.) My just-ended three-week trip (to PNSQC, RubyConf, OOPSLA, and a client site) did special damage. Naturally, I did that damage just as the November issue is being mailed. But next week will be green.

## Posted at 21:48 in category /misc [permalink] [top]

A thought on mocking filesystems

(Sorry about the earlier version of this. I wrote some notes locally and then accidentally synchronized with testing.com.)

Sometimes people mock (or even just stub) some huge component like a filesystem. By doing that, you can test code that uses the filesystem but (1) have the tests run much much faster, (2) not have to worry about cleaning up because the fake filesystem will disappear when the test exits, (3) not have to worry about conflicting with other tests running at the same time, and (4) have more control over the filesystem's behavior and more visibility into its state.

I was listening to someone talk about doing that when I realized that any component like a filesystem has an API that's adequate for a huge number of programs but just right for none of them.

So it seems to me that a project ought to write to the interface they wish they had (typically narrower than the real interface). They can use mocks that ape their interface, not the giant one. There will be adapters between their just-right interface and the giant interface. Those can be tested separately from the code that uses the interface.

Arguing against that is the idea that giant mocks can be shared among projects, thus saving the time spent creating the custom mocks required by my alternative. But I'm inclined to think it's a good practice to write an adapter layer anyway. Without one, it's painful to swap out components: uses of the old component's API are smeared throughout the system.

## Posted at 21:28 in category /coding [permalink] [top]