public static Combine.BinaryCombineDoubleFn ofDoubles() {
    return new SumDoubleFn();
  }
@Test
  public void testSumDoubleFnNegativeInfinity() {
    testCombineFn(
        Sum.ofDoubles(),
        Lists.newArrayList(Double.NEGATIVE_INFINITY, 2.0, 3.0, 4.0),
        Double.NEGATIVE_INFINITY);
  }