new_contents: class Mock(object):
      class _MockQuery(object):
          '''Access Mock internals'''
  
          def __init__(self, mock):
              self._mock = mock
  
          @property
          def attributes(self):
              return set(self._mock._attrs.keys())
  
          @property
          def calls(self):
              return tuple(self._mock._calls)
  
          @property
          def call(self):
              if self._mock._calls:
                  return self._mock._calls[-1]
  
          @property
          def nr_calls(self):
              return len(self._mock._calls)
  
          @property
          def return_(self):
              return self._mock._return
  
          @property
          def except_(self):
              return self._mock._except
  
          @property
          def yield_(self):
              return self._mock._yield_orig
  
      def __init__(self, return_=None, except_=None, yield_=None, **kwargs):
          self._attrs = kwargs
          self._calls = []
          self._return = return_
          self._except = except_
          self._yield_orig = yield_
          self._yield = iter(yield_) if yield_ else None
          self._qry = self._MockQuery(self)
  
      def __getattr__(self, value):
          return self._attrs.setdefault(value, Mock())
  
      def __call__(self, *args, **kwargs):
          self._calls.append((args, kwargs))
          if self._except:
              raise self._except
          if self._yield:
              return self._yield.next()
          if self._return is None:
              self._return = Mock()
          return self._return
  
      @property
      def qry(self):
          return self._qry
  
subject: Add custom Mock class implementation.