So this test stopped passing after adding the length restriction :(

If I inspect event3 just before pushing it to the filter I end up with this

.#<LogAgent::Event:0x00000002444a38 @message_format=nil, @message="# Time: 14", @tags=[], @source_path="", @source_host="holly", @type="", @source_type="", @fields={"mysql_slow_user"=>"alice", "mysql_slow_ip"=>"10.11.11.12", "mysql_slow_query_time"=>3, "mysql_slow_lock_time"=>0, "mysql_slow_rows_sent"=>2, "mysql_slow_rows_examined"=>3224}, @timestamp=2014-03-31 14:05:29 UTC, @uuid="72303710-9bbd-0131-6a20-5404a6423588", @captured_at=2014-04-01 12:19:42 +0100>

Which shows it's truncated the message ... WHY!?!?!!