How to write a program in Haskell, and how to use the Haskell testing tools . . . QuickCheck is a tool written in the functional programming language Haskell that allows testing of specifications by means of randomly generated tests. QuickCheck is part of the standard Haskell library. Re-implementations of QuickCheck exist for many languages, including Ruby and Scheme. SmallCheck is a similar tool, different from QuickCheck in that it tests properties for all finitely many values of a datatype up to some given depth, with progressive increase of depth. Haskell is a research language: many of the testing tools that were first developed for Haskell later find their way to other languages. These slides discuss QuickCheck (two versions), SmallCheck, and some work in progress. We end with some examples of Alloy specifications.