// If updating, make sure to update expected_children below.
  const std::vector<std::string> filenames = {
      GetURIForPath("dir/a_file"),
      GetURIForPath("dir/another_file"),
  };
  for (const auto& filename : filenames) {
    std::unique_ptr<WritableFile> file;
    status = env_->NewWritableFile(filename, &file);
    if (!status.ok())