TDD: Show Your Work Designs

I was reading Brian Marick's write up of his experience with Hillel Wayne's budget modeling experiment.  

Toward the end of the exercise, Marick writes:

I decided to write an affordability function that would call the same functions as can_afford? but return rich results instead of funneling all the possibilities into true or false....  Then I wrote can_afford? in terms of affordability.

I've seen this pattern a number of times recently.  It came up during a transport tycoon exercise,  where I started exploring the idea of generating a complete report of a simulation, and then extracting from that report the answer to the simple question.

Before that, it appeared when I started using kitchen sink logging in my AWS Lambda functions; the event handler produces a record of all of the information it has collected along the way, one field of which is "the answer".  The log entry for the request get a detailed document of all of the (not secret) information, and we can later carve that information into smaller pieces.

What the pattern reminds me of is STEM exams in high school; writing out the derivation of the answer long form, with the final calculation circled at the bottom.  The motivation is, I think, much the same; the view of the intermediate calculations is an important diagnostic tool when the final answer indicates a fault.

GeePaw Hill has recently been discussing the Made application and the Making application.  The Made application provides narrow, targeted affordances, designed to delight the end user who pays the bills.  But the purpose of the Making application is delightful (cost effective) making, where the human in the loop has different concerns.

Injecting the Making into the Made gives us, perhaps, the best of both worlds.

I also see similarity between this idea and Ward Cunningham's early description of technical debt; the underlying report is going to be more closely aligned with how we think about the domain than the simple distillation of the answer, and with the long form design in place, we have code that is aligned with the business, and should be easy to change when the business expects the code to be easy to change.