The server can start like this:

./mongod --auth --setParameter trafficRecordingDirectory=/data/db/job0/mongorunner/traffic_recording --setParameter AlwaysRecordTraffic=notARealPath --setParameter enableTestCommands=0

But this will (correctly) fail:

./mongod --auth --setParameter trafficRecordingDirectory=/data/db/job0/mongorunner/traffic_recording --setParameter AlwaysRecordTraffic=notARealPath
BadValue: Bad value for parameter "AlwaysRecordTraffic": setParameter: 'AlwaysRecordTraffic' is only supported with 'enableTestCommands=true'
try '/home/sajack/mongo/mongod --help' for more information