you'd only do it for a few seconds, not to run it for minutes, i have a fitting to block the oil feed for such testing and a non turbo manifold, not everyone has the bits needed to test properly.
i've not tested this on mfi, but removing the oil cap and letting it flow into there instead will cause a leak in the seal of the system and wouldn't run right then either.
it's just a method of testing the engine without the need of a leak down test as compression tests aren't always conclusive either.

ideally you need to use a non turbo manifold and simulate the same conditions without a turbo and see what happens, i had an engine which on compression tests seemed fine but on a run showed a problem due to engine load conditions.