public static <T> Iterables<T> iterables() {
    return new Iterables<>();
  }
@Test
  @Category(ValidatesRunner.class)
  public void testFlattenIterablesCollections() {
    Set<String> linesSet = ImmutableSet.copyOf(LINES);

    PCollection<Collection<String>> input =
        p.apply(
            Create.<Collection<String>>of(linesSet)
                .withCoder(CollectionCoder.of(StringUtf8Coder.of())));

    PCollection<String> output = input.apply(Flatten.iterables());

    PAssert.that(output).containsInAnyOrder(LINES_ARRAY);

    p.run();
  }