Add test for utility function json_error_message()
Add test for utility function json_error_message()

UUDigitalHumanitieslab/texcavator,msassmann/texcavator,UUDigitalHumanitieslab/texcavator,UUDigitalHumanitieslab/texcavator,msassmann/texcavator,msassmann/texcavator,msassmann/texcavator