anchor.diff:  
     String createdTreeSha;
     String createdCommitSha;
  -
   
     GitHub github;
     RepositorySlug slug;
  
positive.code:   });
  
    test('create and get a new reference (branch)', () {
      return github.git
          .createReference(slug, 'refs/heads/my-branch', createdCommitSha)
          .then((createdRef) {
        return github.git.getReference(slug, 'heads/my-branch');
      }).then((fetchedRef) {
        expect(fetchedRef.ref, equals('refs/heads/my-branch'));
        expect(fetchedRef.object.type, equals('commit'));
        expect(fetchedRef.object.sha, equals(createdCommitSha));
      });
    });
  
    test('create and get a new tag', () {
      String createdTagSha;
  
      var newTag = new CreateGitTag('v0.0.1', 'Version 0.0.1', createdCommitSha,
          'commit', new GitCommitUser('aName', 'aEmail', new DateTime.now()));
  
      // createTag()
  
negative.code:       // getTag()
        return github.git.getTag(slug, createdTagSha);
      }).then((fetchedTag) {
        expect(fetchedTag.tag, equals(tagName));
        expect(fetchedTag.sha, equals(createdTagSha));
        expect(fetchedTag.message, equals('Version 0.0.1'));
        expect(fetchedTag.tagger.name, equals('aName'));
  