Given that yellow rocket is also a member of the brassica family, it is sometimes hard to tell the difference between it and many other members of the brassica group. It can look very, very similar to wild mustard, and many others. Close inspection of the leaves and flowers can help distinguish it from the other brassicas, but the big picture is that you don't really want any of those plants setting seed in your plot, be it yellow rocket, wild mustard, or ppt.