    @Test(expected = IllegalArgumentException.class)
    public void shouldThrowAnExceptionForUnknownEventFlag() {

        final IEXPriceLevelUpdateMessage iexPriceLevelUpdateMessage = anIEXPriceLevelUpdateMessage()
                .withIEXEventFlag(null)
                .build();
        final IEXOrderBook orderBook = new IEXOrderBook(TEST_SYMBOL);

        orderBook.priceLevelUpdate(iexPriceLevelUpdateMessage);
    }