public static DistributionData singleton(long value) {
    return create(value, 1, value, value);
  }
@Test
  public void testSingleton() {
    DistributionData data = DistributionData.singleton(5);
    assertEquals(5, data.sum());
    assertEquals(1, data.count());
    assertEquals(5, data.min());
    assertEquals(5, data.max());
  }