For every rule checked by the automatic referees (see the official ssl rules for details), there is one folder containing both positive and negative tests for that rule.
Every test consists of one log file (see https://ssl.robocup.org/game-logs/ for the format description) and one JSON file encoding a protobuf packet describing the desired event in the log file. They are matched by the file name, differing only in the ending (.log vs .json). The JSON files contain a JSON serialized version of a DesiredEvent packet as described in desired_event_description.proto.