Documentation: Add a section for devlink-trap testing

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/devlink-trap.rst

@@ -196,3 +196,13 @@ narrow. The description of these groups must be added to the following table:
    * - ``buffer_drops``
      - Contains packet traps for packets that were dropped by the device due to
        an enqueue decision
+
+Testing
+=======
+
+See ``tools/testing/selftests/drivers/net/netdevsim/devlink_trap.sh`` for a
+test covering the core infrastructure. Test cases should be added for any new
+functionality.
+
+Device drivers should focus their tests on device-specific functionality, such
+as the triggering of supported packet traps.