@Override
  public Object clone() {
    try {
      ValueString retval = (ValueString) super.clone();
      return retval;
    } catch ( CloneNotSupportedException e ) {
      return null;
    }
  }
@Test
  public void testClone() {
    ValueString vs = new ValueString( "Boden" );

    ValueString vs1 = (ValueString) vs.clone();
    assertFalse( vs.equals( vs1 ) ); // not the same object, equals not implement
    assertTrue( vs != vs1 ); // not the same object
    assertEquals( vs.getString(), vs1.getString() );
  }