@Test
  public void test() {
    // test car won't add fuel if not rented
    assertEquals(0, car1.addFuel(30));

    car1.setRentalStatus(true);
    car1.drive(50);
    int a = car1.addFuel(10);
    car1.drive(50);
    int b = car1.addFuel(5);

    // Check car will only add fuel to full capacity if given
    // right amount and too much.

    assertEquals(a, b);

    car2.setRentalStatus(true);
    car2.drive(50);
    a = car1.addFuel(10);
    car2.drive(50);
    b = car1.addFuel(5);

    assertEquals(a, b);
  }