The best way to test a service is to create an environment which is as close to its ‘real life’ environment as possible.
Ask your product owner to recruit a group of users (preferably ones who will use your service when it goes live).
Ask your users to try and complete specific tasks without your help. If they do something you don’t expect, write it down. If they get stuck, ask them what they are trying to do and write that down. If they get bored or confused, write that down too.
It’s important to interview your users after their experience. They may have a gut instinct about the look and feel, or have questions you haven’t picked up on. Encourage everyone who takes part to be as honest (and critical) as possible.
It’s also worth asking your core feedback team to ‘try and break it.’ This means doing everything they can to try and cause errors, break into the system, or generally cause havoc. It’s good to have a group of people doing this at the same time – just to see how strong your system is. Don’t worry if a lot of things go wrong here. The more things go wrong now, the less bugs and fixes you will have to deal with after go-live.