We have had methods of providing thrust in space without using rockets since 1916, the year the first ion thruster was built. Both use electricity to produce thrust.
Note, for the record, that an ion thruster IS a rocket - it shoots mass out the back (ions, in this case, accelerated electricly) just like any other rocket.
Note that if this EM drive pushes photons out the back, it is also a rocket. However, what I've read on the subject says it doesn't push photons out the back (not even microwave photons), so it's either something unexpected, or a huge steaming pile.
I'll be interested in the first deep-space probe built to test this thing. Should be simple enough - solar panels for power, EM-Drive for push, a comm-channel or six, and something to announce its presence, so we can determine its velocity relative to Earth at all times. If it accelerates, we win. If not, we wasted the cost of a (small) satellite....