code: def test_ref_calc(
      self,
      total_n,
      alt_n,
      p_error,
      max_gq,
      expected_likelihoods,
      expected_gq,
  ):
      caller = PlaceholderVariantCaller(p_error, max_gq)
      gq, likelihoods = caller.reference_confidence(
          total_n - alt_n, total_n
      )
      npt.assert_allclose(expected_likelihoods, likelihoods, atol=1e-6)
      self.assertEqual(expected_gq, gq)
  
imports: from unittest import mock
  from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  import numpy.testing
  from third_party.nucleus.util import variant_utils
  from third_party.nucleus.util import variantcall_utils
  from deepvariant import testdata
  from deepvariant import variant_caller
  from deepvariant.protos import deepvariant_pb2
label_desc: Use image node_id 2 for calling the VariantCallerTests obj's underlying member method code with example usage: obj.test_ref_calc(total_n, alt_n, p_error, max_gq, expected_likelihoods, expected_gq) without return types