Not just for DPS they need one for tanking and healing too. Tanks and healers need to be able to push themselves the same as DPS.

The DPS challenge would be how high you can push your damage as well as managing your threat on the targets as to not pull aggro. The tank challenge should be rotation of cooldowns and managing threat on all targets as well as facing AOE away from the NPC helpers(NPC helpers because it's a party scenario ). The healer challenge should be aiding in DPS, managing threat and keeping tanks and DPS alive.

I hope that is sort of how the trials will be for all three roles anyway. You need to remember that tanking and healing are important for people to do their absolute best on as well.