anchor.diff:      }).then((_) {
         // Create a reference for the tag.
         return github.git
  -          .createReference(slug, 'refs/tags/v0.0.1', createdTagSha);
  +          .createReference(slug, 'refs/tags/$tagName', createdTagSha);
       });
     });
   }
  +
  +String _randomGitName() {
  +  var now = new DateTime.now().toIso8601String().replaceAll(':', '_');
  +
  +  return now.toString();
  +}
  
positive.code: 
    String createdTreeSha;
    String createdCommitSha;
  
  
    GitHub github;
    RepositorySlug slug;
  
negative.code:   });
  
    test('create and get a new reference (branch)', () {
      var branchName = _randomGitName();
  
      return github.git
          .createReference(slug, 'refs/heads/$branchName', createdCommitSha)
          .then((createdRef) {
        return github.git.getReference(slug, 'heads/$branchName');
      }).then((fetchedRef) {
        expect(fetchedRef.ref, equals('refs/heads/$branchName'));
        expect(fetchedRef.object.type, equals('commit'));
        expect(fetchedRef.object.sha, equals(createdCommitSha));
      });
    });
  
    test('create and get a new tag', () {
      var tagName = 'v${_randomGitName()}';
  
      String createdTagSha;
  
      var newTag = new CreateGitTag(tagName, 'Version 0.0.1', createdCommitSha,
          'commit', new GitCommitUser('aName', 'aEmail', new DateTime.now()));
  
      // createTag()
  