@Override
  public Iterable<FileSystem<?>> fromOptions(@Nonnull PipelineOptions options) {
    checkNotNull(options, "Expect the runner have called FileSystems.setDefaultPipelineOptions().");
    return ImmutableList.of(new GcsFileSystem(options.as(GcsOptions.class)));
  }
@Test
  public void testServiceLoader() {
    for (FileSystemRegistrar registrar :
        Lists.newArrayList(ServiceLoader.load(FileSystemRegistrar.class).iterator())) {
      if (registrar instanceof GcsFileSystemRegistrar) {
        Iterable<FileSystem<?>> fileSystems =
            registrar.fromOptions(PipelineOptionsFactory.create());
        assertThat(fileSystems, contains(instanceOf(GcsFileSystem.class)));
        return;
      }
    }
    fail("Expected to find " + GcsFileSystemRegistrar.class);
  }