def METHOD_NAME(self, file_num=1000):
    files = {}  # key -> etag
    for _ in range(file_num):
        key = KEY_PREFIX + random_string(16)
        result = self.s3.put_object(Bucket=env.BUCKET, Key=key, Body=random_bytes(16))
        self.assert_put_object_result(result=result)
        files[key] = result['ETag'].strip('"')
    return files