@Test(expected = InvalidTransformException.class)
public void testInvert() {

  final ValidatingTransform vt1 = new ValidatingTransform();
  vt1.setScale(2);
  vt1.invert(null); // good
  // a little chicanery to get around other checks.
  ((Vector3) vt1.getScale()).setX(0);
  vt1.invert(null); // bad
}