@Test
public void shouldUseExistingAtTimestampHeaderInTimestampedEvent() {

  SimpleEvent base = new SimpleEvent();
  Map<String, String> headersWithTimestamp = Maps.newHashMap();
  headersWithTimestamp.put("@timestamp", "-999");
  base.setHeaders(headersWithTimestamp );
  TimestampedEvent timestampedEvent = new TimestampedEvent(base);
  assertEquals(-999L, timestampedEvent.getTimestamp());
  assertEquals("-999", timestampedEvent.getHeaders().get("@timestamp"));
  assertNull(timestampedEvent.getHeaders().get("timestamp"));
}