public static ComposeCombineFnBuilder compose() {
    return new ComposeCombineFnBuilder();
  }
@Test
  public void testDuplicatedTagsWithContext() {
    expectedException.expect(IllegalArgumentException.class);
    expectedException.expectMessage("it is already present in the composition");

    TupleTag<UserString> tag = new TupleTag<>();
    CombineFns.compose()
        .with(new GetUserStringFunction(), new ConcatStringWithContext(null /* view */), tag)
        .with(new GetUserStringFunction(), new ConcatStringWithContext(null /* view */), tag);
  }