HashMap containsKey

Hi I'm trying to run some junit tests but I have a problem with HashMaps, basically I have to create a RentalAgency for cars So I have

  public class RentalAgencyTest{
    private List<Vehicle> theVehicles;
    private Map<Client,Vehicle> rentedVehicles;
    private RentalAgency renault;
    private Vehicle twingo;
    private Vehicle punto;
    private Client client1;
    private Client client2;
  }

  @Before
  public void before(){
    this.theVehicles = new ArrayList<Vehicle>();
    this.rentedVehicles = new HashMap <Client,Vehicle>();
    this.renault = new RentalAgency(theVehicles, rentedVehicles);
    this.punto = new Vehicle("Fiat", "punto", 2000, 6);
    this.twingo = new Vehicle("Renault", "twingo", 1998, 4);
    this.client1 = new Client("Pignon", 21);
    this.client2 = new Client("Leblanc", 21);
   }

And the problem is with this Test :

@Test
public void testAllRentedVehicles(){
  this.rentedVehicles.put(this.client1, this.punto);
  this.rentedVehicles.put(this.client2, this.twingo);
  assertTrue(this.rentedVehicles.containsKey(this.twingo));
  assertTrue(this.rentedVehicles.containsKey(this.punto));
  assertTrue(this.rentedVehicles.size() == 2);
}

With some workaround I figured that the assert on the size is true, so the rentedVehicles hashmap has 2 vehicles indeed but it doesn't seems like the keys are this.twingo and this.punto as I expected it to be and I can't figure out why or what are they