@Test
  public void testMeanCalculation() {
    Mean a = new Mean();
    a.add(1);
    assertEquals(1, a.count());
    assertEquals(1d, a.mean(), 0.00001d);

    a.add(1);
    assertEquals(2, a.count());
    assertEquals(1d, a.mean(), 0.00001d);
    a.toString();

    Mean b = new Mean();
    b.add(0.5);
    assertEquals(1, b.count());
    assertEquals(0.5d, b.mean(), 0.00001d);

    b.add(2);
    assertEquals(2, b.count());
    assertEquals(1.25d, b.mean(), 0.00001d);
    b.toString();

    Mean c = new Mean();
    assertEquals(0, c.count());
    assertEquals(0d, c.mean(), 0.00001d);
    c.toString();
  }