You can't do that in reality, because if the single engine at one side failed, the aircraft will lose all thrust from that side and can't be balanced, thus the aircraft will be in extreme danger. I think they will use a modified 747 to conduct the test, as it's the biggest quad engine platform they can get.
Also, I don't think they will develop a dual engine Y-20C using two CJ-2000 equivalents, as a quad engine transport plane has more redundancy and could bear a single engine failure (e.g. being hit by an AAM or SAM) when operating near frontlines.
Okay, a couple of things on that.
1) all the modern airliners operate with 2 large engine and are expected to be able to land if one engine fails.
2) this is only for testing. This is not how Y-20 will use in production.