code: def variant_matches_reference_sequence(variant, ref_seq_on_transcript, strand):
      
      if strand == "-":
          ref_seq_on_transcript = reverse_complement_dna(ref_seq_on_transcript)
      return ref_seq_on_transcript == variant.ref
docs: Make sure that reference nucleotides we expect to see on the reference
      transcript from a variant are the same ones we encounter.