diff --git a/AGENTS.md b/AGENTS.md
index 05e8c49e71a9..864466d5a3fa 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -52,6 +52,8 @@ Real-time analytics database. Java, Maven, multi-module project.
 
 ## Running Tests
 
+Use JUnit 5 (`org.junit.jupiter`) for new test classes and for new test methods added to existing JUnit 5 classes. Before adding a JUnit 5 method to an existing JUnit 4 (`org.junit`) class, migrate the class and its module to JUnit 5; otherwise, keep the new method in JUnit 4 until that migration is complete.
+
 Use these flags for faster tests: `-Pskip-static-checks -Dweb.console.skip=true -T1C`
 
 **Single test method:**