Good question.
Unfortunately, I'm unaware of any standard for QoS testing.
Lack of such a standard might because so much is dependent on actual use cases. For example, what's acceptable for HTTP, FTP, NetBeui, Telnet, etc.?
Some traffic kinds, though, do have minimum performance requirements like VoIP's latency, jitter and packet loss. VoIP might also use its MOS as a quality metric.