@Test
 public void testEquals_notEqual() {
   Coordinate c1 = new Coordinate(3, -2);
   Coordinate c2 = new Coordinate(-2, 3);
   assertFalse(c1.equals(c2));
 }
 @Test
 public void testEquals_equal() {
   Coordinate c1 = new Coordinate(6, -2);
   Coordinate c2 = new Coordinate(6, -2);
   assertTrue(c1.equals(c2));
 }