OUnit is a unit test framework for OCaml. It allows one to easily create unit-tests for OCaml code. It is based on HUnit, a unit testing framework for Haskell. It is similar to JUnit, and other XUnit testing frameworks.
Adam Cimarosti created a 10 minute tutorial video on how to start using OUnit. In the video Adam creates a new test suite from scratch, and explains what he is doing. Have a look: