code: def test_valid(self):
      docker_config.DockerConfig(
          parent_image="tensorflow/tensorflow:latest-gpu",
          image_build_bucket="test-bucket",
          image="gcr.io/test-project/tf_cloud_train:1",
          cache_from="gcr.io/test-project/tf_cloud_train:0",
      )
  
imports: from absl.testing import absltest
  from tensorflow_cloud.core import docker_config
label_desc: Use image node_id 1 for calling the TestDockerConfig obj's underlying member method code with example usage: obj.test_valid() without return types