Add release notes wrt #51

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -12,7 +12,8 @@ Modules:
 
 2.19.0 (not yet released)
 
--
+#51: Unify testing structure/tools to JUnit5 [JSTEP-10]
+ (contributed by Joo-Hyuk K)
 
 2.18.2 (27-Nov-2024)
 2.18.1 (28-Oct-2024)