In another thread, it became clear that the most appropriate fix for this issue in the factory test code is:
On lines 446 and 447, in the function checkI2cAddr():
Change one instance of Wire. to Wire1. one each of the two lines.
Wire.beginTransmission( lastptr->addr );
if ( Wire.endTransmission() == 0 )
...becomes:
Wire1.beginTransmission( lastptr->addr );
if ( Wire1.endTransmission() == 0 )