def METHOD_NAME(self):
    """Read a single-chain structure by ATOM entries.
    Reference:
    http://www.rcsb.org/pdb/files/fasta.txt?structureIdList=1A8O
    """
    chain = SeqIO.read("PDB/1A8O." + extension, parser)
    self.assertEqual(chain.id, "1A8O:A")
    self.assertEqual(chain.annotations["chain"], "A")
    self.assertEqual(chain.annotations["model"], 0)
    self.assertEqual(
        chain.seq,
        "MDIRQGPKEPFRDYVDRFYKTLRAEQASQEVKNWMTETLLVQNANPDCKTIL"
        "KALGPGATLEEMMTACQG",
    )