<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate(cls, mapper_spec):
 """Validates mapper specification. Args: mapper_spec: an instance of model.MapperSpec to validate. Raises: BadWriterParamsError: when Output writer class mismatch. """

    if mapper_spec.output_writer_class() != cls:
      raise errors.BadWriterParamsError("Output writer class mismatch")
    params = output_writers._get_params(mapper_spec)
    # Bucket Name is required
    if cls.BUCKET_NAME_PARAM not in params:
      raise errors.BadWriterParamsError(
          "%s is required for the _HashingGCSOutputWriter" %
          cls.BUCKET_NAME_PARAM)