Property Driven Design: MinMax

I wrote an article on Property Testing about a year ago. Isocpp.org even linked to it which was pretty cool. Recently, I uncovered a fantastic talk by Jessica Kerr about property testing. Kerr’s talk reinvigorated my languid research effort toward generated testing. Kerr presented the idea (novel to me) that properties aren’t rigid. Properties don’t need to exclude all possible incorrect results for a given function. Properties simply must reduce the size of the incorrect space. This may seem like semantics, but it is easier to exclude a wild-ass-guess that verify it is correct. Additionally, some domains may not have a solidly defined answer,a nd the result my be probabilistic in nature. This post will focus on deterministic problems for the moment, but realize that property testing is vastly more general than mundane example testing. How properties reduce the size of the problem space makes me imagine this Figure.

sometimes_code_gives_you_a_wtf

Following Kerr’s references, I found a set of projects from a predicate-logic course. This course provides 20 separate projects excellently cast for a property-driven-design tutorial. These projects are unique since besides the typical requirements they enumerate the predicate functions each requirement typifies. Predicate functions are to a predicate-logician as properties are to a computer scientist. These enumerated properties (predicates) clarified many points I misunderstood about property testing.

This post will step through the design of the first project minmax using C++. My primary goal for this article is to address a concern raised by a colleague, “Does pulling in more complexity — a fancy test generator — actually increase quality?”