Yes testing a sub system when there are numerous lockouts can be problematic. But I found in many situations if not most all testing of upgrades or repairs should be scheduled after all systems repairs were complete then done in a system by system order there were exceptions when certain coordinated systems could be isolated and tested or in some cases a sub was required to be online in order to complete other repairs or construction. Other times when a contractor had completed their scope of work it was far better to halt other work, have the workers clear their materials temporarily bring the completed system online for testing purposes and sign off on the work allowing the contractor to move on possibly leaving one or their staff members on site in case further integration was required
Having a wall sized production schedule time table and progress flow chart in the Senior Engineer's or job superintendent's shack was one of the most valuable tools on a construction site.