In the last article we learned how to generate objects with Java 8 in a functional way and implemented a small API based around the Gen monad. Although already powerful on its own, generators really shine when we use them in combination with property-based testing. A property-based test verifies a statement about the output of your code based on some given input. The same statement - or property - is verified for many different possible inputs to find one that falsifies the property. This article builds upon the implementation of Gen and discusses a simple API that enables us to write property-based tests.

I recently had the chance to toy around with property-based testing. Property-based tests verify statements about the output of your code based on some input, where the same statement is verified for many different possible (admissible and inadmissible) inputs. Such tests rely heavily upon randomly generated objects and values. Even if you do not fully commit to property-based testing, having abstractions for generating random objects and values from your domain can simplify testing a lot. This article shows how to build a simple generator-based approach that plays well along with property-based testing and can simplify your test cases tremendously.

Recursion is a topic discussed in chapter 2 of Functional Programming in Scala by Chisuano and Bjarnason. In this short post, I explore this topic from a different angle, discussing how we can get from a mathematical definition of the recurrence to a tail-call-optimized implementation.