Unit Test Framework (vastly simpler than JUnit)
If your unit tests aren't passing, it might make you easily annoyed, or marked by impatence or ill humor. But unit tests are extremely valuable, and learning about them is an important part of a computer science curriculum.
A popular tool for unit testing is JUnit, from https://junit.org/. It works well, but it's a large and complex tool. It also makes extensive use of reflection to identify and invoke tests. It's an understandable use of reflection, but now that Java has lambdas, normal Java techniques can easily be used to build a list of tests to be executed, instead of making a new set of extra-lingual rules using annotations and reflective access.
In an introductory course on OO programming, for example, it's better to limit the number of new concepts students are exposed to down to a manageable set. Something much simpler than JUnit is called called for. Testy is intended to fulfill that need.