Just curious, have you done this^^^? Must make a mess huh?They make a gauge that threads In place of the oil filter.
Or you could take the filter off of it, put a deep pan under it and have a buddy start it up. If you don’t have any flow within 3 seconds then you have a problem.
It’s not the best method but would work. Obviously somone needs to man the key and shut it off pretty damn quick.
If you have a lot of flow, try a new oil filter (process of elimination)