I've read that quote on a couple of different occasions, and don't see a conflict. Of course you want to prepare engines to pass the tests, and in fact, make any ECOs to make that work.
Every airplane prototype goes through exactly that.
He shouldn't also be conducting the test. That's the conflict.
The wider conflict is that you cannot be employed by the testee and still a reliable tester. That's why we don't let people give themselves driving licenses for instance.
Every airplane prototype goes through exactly that.