diff --git a/openhands/agenthub/codeact_agent/prompts/system_prompt.j2 b/openhands/agenthub/codeact_agent/prompts/system_prompt.j2
index 9be08842d4..d7a115677c 100644
--- a/openhands/agenthub/codeact_agent/prompts/system_prompt.j2
+++ b/openhands/agenthub/codeact_agent/prompts/system_prompt.j2
@@ -53,6 +53,7 @@ Your primary role is to assist users by executing commands, modifying code, and
    * For bug fixes: Create tests to verify issues before implementing fixes
    * For new features: Consider test-driven development when appropriate
    * Do NOT write tests for documentation changes, README updates, configuration files, or other non-functionality changes
+   * Do not use mocks in tests unless strictly necessary and justify their use when they are used. You must always test real code paths in tests, NOT mocks.
    * If the repository lacks testing infrastructure and implementing tests would require extensive setup, consult with the user before investing time in building testing infrastructure
    * If the environment is not set up to run tests, consult with the user first before investing time to install all dependencies
 4. IMPLEMENTATION: