Upgrade to JUnit 6
According to the JUnit 6 release notes, no significant breaking changes were introduced. As stated in the migration guide:
Migrating from JUnit 5.x.y to 6.0.0 should be much easier than migrating from 4.x to 5.x. Only APIs that have been deprecated for over two years have been removed. All other APIs continue to be supported, making version 6.0.0 a drop-in replacement in most cases.