@Override
  public String toString() {
    var roles = Arrays.toString(this.roles.keySet().toArray());
    return "Customer{roles=" + roles + "}";
  }
@Test
  void toStringTest() {
    var core = new CustomerCore();
    core.addRole(Role.BORROWER);
    assertEquals("Customer{roles=[BORROWER]}", core.toString());

    core = new CustomerCore();
    core.addRole(Role.INVESTOR);
    assertEquals("Customer{roles=[INVESTOR]}", core.toString());

    core = new CustomerCore();
    assertEquals("Customer{roles=[]}", core.toString());
  }