### Question:
User implements IUser { @Override public int hashCode() { int result = (initialized) ? id : 0; result = 19 * result + name.hashCode(); result = 19 * result + firstName.hashCode(); return result; } User(String aName, String aFirstName); int getId(); void setId(int anID); List<Rental> getRentals(); void setRentals(List<Rental> someRentals); String getName(); void setName(String aName); String getFirstName(); void setFirstName(String aFirstName); Calendar getBirthdate(); double getCharge(); @Override boolean equals(Object o); @Override int hashCode(); boolean hasRentals(); int addRental(Rental rental);  }### Answer:
@Test public void testHashCode() throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException { IUser x = new User(NAME, FIRSTNAME); IUser y = new User(NAME, FIRSTNAME); assertEquals(x.hashCode(), y.hashCode()); x.setId(42); assertTrue(x.hashCode() != y.hashCode()); y.setId(42); assertEquals(x.hashCode(), y.hashCode()); }