code: def simple_test_pair(ratings, n_users=1000, n_rates=5, f_rates=None):
      """
      Return a single, basic train-test pair for some ratings.  This is only intended
      for convenience use in test and demos - do not use for research.
      """
  
      if f_rates:
          samp = SampleFrac(f_rates)
      else:
          samp = SampleN(n_rates)
  
      train, test = next(sample_users(ratings, 1, n_users, samp))
  
      return train, test
  
imports: from collections import namedtuple
  import logging
  from abc import ABC, abstractmethod
  import numpy
  import pandas
  from seedbank import numpy_rng
label_desc: Use image node_id 7 for calling a global function with example usage: simple_test_pair(ratings, n_users, n_rates, f_rates) and returns: train,  test