anchor.diff:            final match = _lsRemoteRegExp.allMatches(line).single;
             assert(match.groupCount == 2);
   
  -          return new GitReference(match[1], match[2]);
  +          return new CommitReference(match[1], match[2]);
   
           }).toList();
     }
  
positive.code:       'GitReference: $reference  $sha';
  }
  
  class BranchReference extends GitReference {
    static const _localBranchPrefix = r'refs/heads/';
  
    final String branchName;
  
negative.code: /**
   * Represents the output from `git ls-remote`
   */
  class CommitReference {
    final String sha;
    final String reference;
  
    CommitReference(this.sha, this.reference) {
      assert(Git.isValidSha(sha));
  
      assert(reference != null);
  