Can't make the "aggregate" filter to work

Hi there,

I'd like to use aggregate filter to gather informations from different log lines, but I'm not able to make it write anything in the logs.

I tried to add the following lines in my logstash configuration :

filter {
    aggregate { task_id=>"test" code=>"event['test']='OK'" }

but the test field is not added in my logs.
According to the documentation this should work that way, right ?

Thanks for your help

(Note : I use logstash v 2.0)