class_docstr: Test io.SamReader on CRAM formatted files.
code: def test_header(self, filename, has_embedded_ref):
      with self._make_reader(filename, has_embedded_ref) as reader:
          self.assertEqual(reader.header.format_version, "1.3")
          self.assertEqual(
              [contig.name for contig in reader.header.contigs],
              ["chrM", "chr1", "chr2"],
          )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import itertools
  from absl.testing import absltest
  from absl.testing import parameterized
  import six
  from etils import epath
  from third_party.nucleus.io import sam
  from third_party.nucleus.io import tfrecord
  from third_party.nucleus.protos import reads_pb2
  from third_party.nucleus.protos import reference_pb2
  from third_party.nucleus.testing import test_utils
  from third_party.nucleus.util import ranges
label_desc: Use image node_id 2 for calling the CramReaderTests obj's underlying member method code with example usage: obj.test_header(filename, has_embedded_ref) without return types