With dual engine airframes, the usual engine test approach is to just bolt the test engine nacelle to a pylon that juts out from the side of the main fuselage.

With dual engine airframes, the usual engine test approach is to just bolt the test engine nacelle to a pylon that juts out from the side of the main fuselage. It looks absurd, but doesn't compromise the main propulsion and apparently works. One of many examples: https://theaviationist.com/2012/05/10/dont-worry-this-weird-plane-with-5-engines-is-just-a-flying-test-bed-for-a-quite-innovative-fod-resistant-engine/ https://theaviationist.com/2012/05/10/dont-worry-this-weird-...