code: def test_make_population_vcf_readers_with_one_vcf(self):
      filenames = [testdata.AF_VCF_CHR20_AND_21]
  
      output = allele_frequency.make_population_vcf_readers(filenames)
  
      self.assertIsInstance(output["chr20"], vcf.VcfReader)
      self.assertIsInstance(output["chr21"], vcf.VcfReader)
      self.assertIsInstance(output["chr22"], vcf.VcfReader)
      # All reference names should map to the same VCF that starts with chr20.
      self.assertEqual(next(output["chr20"]).reference_name, "chr20")
      self.assertEqual(next(output["chr21"]).reference_name, "chr20")
      self.assertEqual(next(output["chr22"]).reference_name, "chr20")
  
file_path: deepvariant/deepvariant/allele_frequency_test.py
imports: from absl.testing import absltest
  from absl.testing import parameterized
  from third_party.nucleus.io import fasta
  from third_party.nucleus.io import vcf
  from third_party.nucleus.protos import variants_pb2
  from deepvariant import allele_frequency
  from deepvariant import testdata
  from deepvariant.protos import deepvariant_pb2
label_desc: Use image node_id 5 for calling the AlleleFrequencyTest obj's underlying member method code with example usage: obj.test_make_population_vcf_readers_with_one_vcf() without return types