[Beav]

Not necessarily. The ECU can probably 'see' a short to ground or open circuit but what happens if the injector's resistance changes slightly? That would affect the amount of fuel it can flow but probably wouldn't trigger a code as there would still be continuity

If disconnecting each injector, one at a time, caused all cylinders to drop rpm equally either the problem wasn't present at the time or there's a different problem. If one or more cylinders did not change rpm then it is necessary to determine if spark, fuel or air is the culprit.