JUnit is composed of several different modules from three different sub-projects.

JUnit 6.1.3 = JUnit Platform + JUnit Jupiter + JUnit Vintage

JUnit Jupiter is the combination of the programming model and extension model for writing JUnit tests and extensions. The Jupiter sub-project provides a TestEngine for running Jupiter based tests on the platform.

JUnit Vintage provides a TestEngine for running JUnit 3 and JUnit 4 based tests on the platform. It requires JUnit 4.12 or later to be present on the class path or module path. Note, however, that the JUnit Vintage engine is deprecated and should only be used temporarily while migrating tests to JUnit Jupiter or another testing framework with native JUnit Platform support.