@Test
 public void testOverbooking() {
   Cargo cargo1 = newCargo(100);
   Cargo cargo2 = newCargo(9);
   int code = shippingService.makeBooking(cargo1, voyage);
   assertEquals(0, code);
   code = shippingService.makeBooking(cargo2, voyage);
   assertEquals(-1, code);
 }
 @Test
 public void testTooMuch() {
   Cargo cargo1 = newCargo(40);
   Cargo cargo2 = newCargo(40);
   Cargo cargo3 = newCargo(31);
   int code = shippingService.makeBooking(cargo1, voyage);
   assertEquals(0, code);
   code = shippingService.makeBooking(cargo2, voyage);
   assertEquals(1, code);
   code = shippingService.makeBooking(cargo3, voyage);
   assertEquals(-1, code);
 }
 @Test
 public void testOrdinaryBooking() {
   Cargo cargo1 = newCargo(40);
   Cargo cargo2 = newCargo(40);
   Cargo cargo3 = newCargo(20);
   int code = shippingService.makeBooking(cargo1, voyage);
   assertEquals(0, code);
   code = shippingService.makeBooking(cargo2, voyage);
   assertEquals(1, code);
   code = shippingService.makeBooking(cargo3, voyage);
   assertEquals(2, code);
 }