add concatenate trace method and tests for it
add concatenate trace method and tests for it


Former-commit-id: 264c10f131c15bbb05c6679df14a01b127805d15
Former-commit-id: 8f34618c517ad8edfc570a6a45a3dd51f4051f1c
dssg/wikienergy,dssg/wikienergy,dssg/wikienergy,dssg/wikienergy,dssg/wikienergy