//City.java
@Entity
@Table(name="cities")
@GroupSequence({Basic.class, PointOfInterest.class, Extended.class})
public class PointOfInterest implements Serializable {
  @XmlElement(name = "Name", required=true)
  @OneToMany(mappedBy="point", fetch=FetchType.EAGER, cascade={CascadeType.ALL})
  @Size(min=1, groups=Basic.class)
  @Valid
  private List<Name> names = new ArrayList<Name>();
  //...

//Name.java
@Entity
@Table(name="city_nm")
@GroupSequence({Basic.class, Name.class, Extended.class})
public class Name implements Serializable {
  @XmlAttribute
  @NotNull(groups=Basic.class)
  @Size(min=2, max=250, groups=Basic.class)
  @Column(name="city_nm", nullable=false, length=250)
  private String name;
  //...

//CityTests.java
@Test
public void multipleInvalidNames() throws Exception {
  City city = factory.makeCity();
  Name name1 = factory.makeName();
  name1.setName("a"); //Below @Size min!
  city.addName(name1);
  Name name2 = factory.makeName();
  name2.setName("b"); //Also too short!
  city.addName(name2);
  Set<ConstraintViolation<?>> errors = tryPersist(city).getConstraintViolations();
  //...