code: def _validate_units(self, has_units, key, value):
          
          if has_units:
              if isinstance(self.test.units, dict):
                  required_units = self.test.units[key]
              else:
                  required_units = self.test.units
              if not isinstance(value, pq.quantity.Quantity):
                  self._error(key, "Must be a python quantity")
              if not isinstance(value, pq.quantity.Quantity):
                  self._error(key, "Must be a python quantity")
              provided_units = value.simplified.units
              if not isinstance(required_units, pq.Dimensionless):
                  required_units = required_units.simplified.units
              if not required_units == provided_units:
                  self._error(key,
                              "Must have units of '%s'" % self.test.units.name)
docs: Validate fields with `units` key in schema set to True.
  
          The rule's arguments are validated against this schema:
          {'type': 'boolean'}