Ok to minimize cost, I will use the same setup, in that i sum up the total time it takes the all 3 to reach their peaks and use it as check time and during that time no tests are performed and after that time elapses i check which pin of Arduino has not got at least two rising edges and if there is any, that indicates that particular phase in relation to that pin has issues, may be the phase is not present or may be the opto is not functioning and definitely i will have all optocouplers soldered directly no the PCB no IC sockets to minimize intermittent connection issues.