class_docstr: Groupwise RankingEstimator tests.
docstr: Train the estimator for one step and check checkpoint.
docstr_tok: ["Train","the","estimator","for","one","step","and","check","checkpoint","."]
code: def test_train(self):
      """Train the estimator for one step and check checkpoint."""
      self._estimator.train(input_fn=_train_input_fn, steps=1)
      self._assert_checkpoint(expected_global_step=1)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  from absl.testing import parameterized
  import tensorflow
  from tensorflow import estimator
  from tensorflow_ranking.python import feature
  from tensorflow_ranking.python import head
  from tensorflow_ranking.python import losses
  from tensorflow_ranking.python import model
label_desc: Use image node_id 5 for calling the GroupwiseRankingEstimatorTest obj's underlying member method code with example usage: obj.test_train() without return types