test-jid-decode: factor out common code
test-jid-decode: factor out common code

community-ssu/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble