Add module-info.java to have an example that works with Jigsaw too.

[Brixomatic]

Unfortunately this simple example doesn't show how to meaningfully combine JUnit with Jigsaw.
If I'm not mistaken, junit should not be in the "requires" section of the module-info,java, as it is not required by the module, only by its tests.

[sormuras]

Short answer: Create dedidated (project-internal) test modules (that binaries are not published to an external repository).

Or: JUnit should not be a dependency of the main scope, as it is not used by main classes, only by its tests.

Longer answer: https://sormuras.github.io/blog/2018-09-11-testing-in-the-modular-world