JUnit5 is more tolerant regarding the visibility of test classes and methods than JUnit4, which required everything to be public. Test
classes and methods can have any visibility except private. It is however recommended to use the default package visibility to improve
readability.
Test classes, test methods, and lifecycle methods are not required to be public, but they must not be private.
It is generally recommended to omit the public modifier for test classes, test methods, and lifecycle methods unless there is a technical reason
for doing so – for example, when a test class is extended by a test class in another package. Another technical reason for making classes and
methods public is to simplify testing on the module path when using the Java Module System.
— JUnit5 User Guide
What is the potential impact?
The code will be non-conventional and readability can be slightly affected.
Exceptions
This rule does not raise an issue when the visibility is set to private, because private test methods and classes are
systematically ignored by JUnit5, without a proper warning. In this case, there is also an impact on reliability and so it is handled by the rule
S5810.
