@Test(expected = OperationException.class)
public void testInvalidISO8601() throws FieldNotFoundException {

  InternalEvent ievent = new InternalEvent("foo", null, 1);
  DummyStringEvent devent = spy(new DummyStringEvent(""));
  ievent.setEventObj(devent);
  doReturn("note a date string").when(devent).getFieldAsString("foo");
  TimeOperation op = new TimeOperation("foo", TimeFieldType.ISO8601);
  op.perform(ievent);
}