Fair question..don't know how Swiss work but from what I've seen over the years unless there's a compelling reason for a crew change (contract, industrial agreements, impingement on leave, open ended delay) often as not the crew that broke it get to sit it out and fly the aircraft home when it is fixed.
Not sure why the thoughts about test pilot requirements, (unless something really odd went on or it's company policy.). .the post engine test requirement was discussed earlier in the thread.