anchor.diff:  
     Future<String> _runGit(List<String> args, Directory workingDir) {
       return runGit(args, workingDir: workingDir.path).transform((result) {
  -      if (!result.success) throw "Error running git: ${result.stderr}";
  +      if (!result.success) {
  +        throw "Error running: git ${Strings.join(args, ' ')}\n"
  +            "${Strings.join(result.stderr, '\n')}";
  +      }
  +
         return result.stdout;
       });
     }
  
positive.code:       workingDir = rootDir;
        return runGit(['init']);
      }).chain((_) => runGit(['add', '.']))
        .chain((_) => runGit(['commit', '-m', 'initial commit']))
        .transform((_) => workingDir);
    }
  
  
negative.code:     return super.create(parentDir).chain((rootDir) {
        workingDir = rootDir;
        return runGit(['add', '.']);
      }).chain((_) => runGit(['commit', '-m', 'update',
                              '--author="Pub Test <pub@dartlang.org>"']));
    }
  
    /**
  