old_contents: class LaboratoryException(Exception):
      pass
  
  
  class MismatchException(LaboratoryException):
      pass
  
new_contents: class LaboratoryException(Exception):
      def __init__(self, message, *a, **kw):
          self.message = message
          super(LaboratoryException, self).__init__(*a, **kw)
  
  
  class MismatchException(LaboratoryException):
      pass
  
subject: Add message attr to LaboratoryException