Is there a limitation on the length of the message you can use to test a rule? The HZR020I runtime diagnostics message is quite large, and the panel in 2.1 looks like it only supports two lines for a message.
There is not a limit. This message is a multi-line WTO (MLWTO) so it is composed of several lines. To test the current rule on the AOF test environment panel (2.1) enter this message:
HZR0200I TYPES: LOOP:1
This should trigger the rule in the test environment in the same way it will be triggered when the actual message appears.