Wednesday, February 11, 2009

The Second Law of Thermo-Specifications

A couple of days ago, Adam Milligan posted an eponymous "law" on the Pivotal Labs blog.

It includes a corollary stating, "The full definition of correct behavior of code exists in the tests for that code."

Now, there seemed to be something fundamentally off about this proposition ... and I wanted to figure out what that was.

Surely Mr. Milligan doesn't mean this in the trivial, tautological sense (define the spec to be no more than what test cases happen to exist at a point in time) ... even though Agile dogma often borders on that view, pretending it's some kind of paradoxical path to enlightenment like a Zen koan.

The comments to his post start to touch on "spec" vs. "test," and whether 100% test coverage is practical, desirable, or conclusive.

Of course even 100% code coverage, with a missing code path and a matching missing test and behavior spec equals ... test success, and wrong functionality.

In such a case, though, the problem has been externalized from the Agile context and put onto a faceless "business person" who "doesn't get" Agile because he or she actually wants to plan ahead and describe some certain specs that persist over time.

This is a neat trick. In physics, all sorts of magical things can happen if you look only inside of one context (or frame of reference) without looking at what's happening outside, or at what's happening to the frame itself. In finance, there can certainly be a free lunch ... if you can make its cost into an externality and remove it from your model.

Once you make the tests and code-based behavior spec a part of the application you're building -- and clearly, once it's a real cost center as well as a critical deliverable part of the project, you have done so -- then you are in a sense simply externalizing that troublesome human interaction (specification, functional analysis, planning). Yes, the tests match the code under test. But seen at a different level of abstraction, it's just another flavor of interface-driven development, or debugging.

Most engineers would love to realize the dream of self-describing, self-verifying code, whether that description be some kind of formal model, or a textual DSL (as with Microsoft's Oslo), or a set of tests and code-based behavior specs. And, indeed, these systems all improve the transparency of the code, propagating requirements from the outside in, and revealing when they are not met.

But even with the most "bought-in" business stakeholders, it is impossible to escape the the outermost specification layer, the one with the humans in it.

5 comments:

Steve said...

I'm kind of fuzzy on what your point is, but if I'm understanding correctly, you think Adam is saying that if he correctly writes that tests and code to make Word, but that the customer was mistaken in product definition and realizes we should have built Excel, that according to Adam's law we're all still ok - in the broader (not just software development) sense of "ok".

If that's a fair characterization of the above then I'm confident Adam didn't mean that.

gaohui said...

The holidays are a time ed hardy of getting together with friends ed hardy shoes and family, attending elaborate ed hardy clothing parties, and other exciting events ed hardy clothes that involves dressing up in stunning ed hardy store wardrobes. If you ed hardy Bikini are pregnant during ed hardy swimsuits the holidays, it does not ed hardy Caps mean that you are unable buy ed hardy to look fabulous and ed hardy swimwear stylish. Now, an expectant ed hardy sale mother has many styles of chic ed hardy glasses maternity clothing that allows cheap ed hardy her to show off her baby bump Christian audigier while looking spectacular.

Buy Cheap WOW Gold said...

GREAT recipe! I accept started authoritative my own laundry bactericide alone afresh - and adulation it - but don't accept a pretreatment aerosol - These are EASY capacity and I'm traveling to accord this a try!!! Thanks for announcement it!

Anonymous said...

Pet them, snuggle with these, not to mention dog leashes prepare these guys.

For every they make certain that you are unable to permit them to have almost any give diet that you simply can not consume. Incorporate insert them in numerous room in your home although you are drinking all your recipe.

You also need so that you give these items dog boots poorer part in daytime. Of having the unhealthy weight . puppy could be equipped to lose weight is that if there're exercising not to mention having to eat the appropriate way of measuring pet dog collars and leashes foodstuffs. Immediately you're letting them hold the correct amount liquid. It willaids to make sure they're hydrated all through play dog leashes time.

summerlijia said...

Guys, do you like to play MMORPG? Guild Wars 2 is one of the most wonderful MMORPGs.I'm a big fan of Guild Wars 2 and good at farming Guild Wars 2 gold. I know a good website to update game guidance about how to farm gold. The cheap Guild Wars 2 gold is also available in that store. So, if you lack gold, you can have a try of that store. Just click the colored word which will direct you.