@Test
public void testToString() {

  assertTrue(a.toString().equals(
      "mean:2.0 stdev:1.0 var:1.0 cNA:0 count:3 min:1.0 max:3.0"));
  assertTrue(d.toString().equals(
      "mean:4.5 stdev:3.08 var:9.5 cNA:3 count:6 min:1.0 max:9.0"));
}