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

  InternalEvent ievent = new InternalEvent("foo", null, 1);
  DummyStringEvent devent = spy(new DummyStringEvent(""));
  ievent.setEventObj(devent);
  doReturn("-1").when(devent).getFieldAsString("foo");
  TimeOperation op = new TimeOperation("foo", TimeFieldType.SECONDS);
  op.perform(ievent);
}