@Test
public void testInterceptHttpListener() {

  EventListener caller = mock(EventListener.class);
  HttpSessionEvent event = mock(HttpSessionEvent.class);
  @SuppressWarnings("unchecked")
  Set<Object> listenerSet = mock(Set.class);
  HttpSession session = mock(HttpSession.class);
  when(session.getServletContext()).thenReturn(servletContext);
  when(servletContext.getAttribute(SessionHelpers.INTROSPECTING_LISTENERS)).thenReturn(listenerSet);
  when(event.getSession()).thenReturn(session);
  sessionHelpers.interceptHttpListener(caller, event);
  verify(listenerSet).add(caller);
}