Giorgio Sironi has a new post to his site today talking about a method (and tool) around a different sort of testing practice: property-based testing. The difference is that, instead of hard-coding values and evaluating them post-processing, you're generating random values and ensuring they match against a set of properties, not values.

I'm a great advocate of automated testing and of finding out your code does not work on your machine, 30 seconds after having written it, instead of in production after it has caused a monetary loss and some repair work to be performed. [...] However, classic test suites written with xUnit and BDD styles have some scaling problems they hit when you want to exercise more than some happy paths. [...] Property-based testing is an approach to testing coming from the functional programming world.

He helps to make the point a bit more clear with an example of testing the "sort" function and its results. He talks about how to test it using normal data, empty data, etc. but notes that this kind of testing can become "boring and error-prone". Instead he proposes the property-based testing of the results. He generates random values to feed into the method and checks to ensure the results are sorting by comparing them to each other. He expands this with a bit more complex example, showing how to test some DateTime handling and evaluating the result with logic in a closure. To help make this kind of testing easier, he's created a library (Eris) that extends PHPUnit and provides the methods seen in his examples.