Testing JUnit 5 classes of a JPMS-enabled project with Surefire may fail if a test class (or, for example, an abstract test base class) is not declared "public". I'm seeing the following error:
This could be fixed by adding the recommended "opens some.package" to the project's module-info.java, however that is undesirable since it changes the project's behavior beyond just unit testing. Adding a secondary "test-only" module-info.java is also counterproductive since not all IDEs support this, and these two files would have to be kept in sync, which is non-trivial.
An easy fix would be to change the "-
add-exports" VM parameter that surefire adds automatically to "-add-opens" in maven-surefire-common/src/main/java/org/apache/maven/plugin/surefire/booterclient/ModularClasspathForkConfiguration.java
This bug is particularly bad because PMD now specifically complains about junit5 classes marked as public instead of package-private; see https://pmd.github.io/2021/05/29/PMD-6.35.0/