public void testHashcode() {
        XYCoordinate v1 = new XYCoordinate(1.0, 2.0);
        XYCoordinate v2 = new XYCoordinate(1.0, 2.0);
        assertTrue(v1.equals(v2));
        int h1 = v1.hashCode();
        int h2 = v2.hashCode();
        assertEquals(h1, h2);