@Override
  public SelJodaDateTimeZone assignOps(SelOp op, SelType rhs) {
    if (op == SelOp.ASSIGN) {
      SelTypeUtil.checkTypeMatch(this.type(), rhs.type());
      this.val = ((SelJodaDateTimeZone) rhs).val;
      return this;
    }
    throw new UnsupportedOperationException(type() + " DO NOT support assignment operation " + op);
  }
@Test
  public void testAssignOps() {
    one.assignOps(SelOp.ASSIGN, another);
    assertEquals("DATETIME_ZONE: America/Los_Angeles", one.type() + ": " + one);
  }