@Test
public void testPreserveExisting() throws Exception {

  Context context = new Context();
  context.put(UUIDInterceptor.HEADER_NAME, ID);
  context.put(UUIDInterceptor.PRESERVE_EXISTING_NAME, "true");
  Event event = new SimpleEvent();
  event.getHeaders().put(ID, "foo");
  assertEquals("foo", build(context).intercept(event).getHeaders().get(ID));
}