docstr: Test of stacked parallel ccmbinators.
docstr_tok: ["Test","of","stacked","parallel","ccmbinators","."]
code: def test_parallel_with_zero_counters(self):
      """Test of stacked parallel ccmbinators."""
      dataset1 = lambda: (i for i in range(10))
      dataset2 = lambda: (i for i in range(10, 20))
      dataset3 = lambda: (i for i in range(20, 30))
      parallel = data.Parallel(
          [dataset1, dataset2, dataset3], counters=[1, 0, 1]
      )
      generator = parallel()
  
      self.assertEqual(next(generator), 0)
      self.assertEqual(next(generator), 20)
      self.assertEqual(next(generator), 1)
      self.assertEqual(next(generator), 21)
      self.assertEqual(next(generator), 2)
      self.assertEqual(next(generator), 22)
      self.assertEqual(next(generator), 3)
      self.assertEqual(next(generator), 23)
  
imports: import itertools
  import os
  from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from trax import data
label_desc: Use image node_id 19 for calling the InputsTest obj's underlying member method code with example usage: obj.test_parallel_with_zero_counters() without return types