The following versions of PortletMVC4Spring were released on May 4, 2020 AD:
For download coordinates and archetype usage, see the project's README.md document.
At the time of this writing and the release of the aforementioned versions, there are no significant differences between the source files of the master (5.2.x) and 5.1.x branches. The main purpose of having two branches is for the convenience of testing with two different versions of the Spring Framework.
MVCS-43: Breaking Change in the com.liferay.portletmvc4spring.test-5.2.1.jar module
The com.liferay.portletmvc4spring.test module (contains classes like MockPortletRequest, MockPortletResponse, etc.) has undergone a breaking-change package name refactor. For more information, see MVCS-43.