public NetworkClient.InFlightRequest completeLastSent(String node) {
        NetworkClient.InFlightRequest inFlightRequest = requestQueue(node).pollFirst();
        inFlightRequestCount.decrementAndGet();
        return inFlightRequest;
    }
@Test
    public void testCompleteLastSentThrowsIfNoInFlights() {
        assertThrows(IllegalStateException.class, () -> inFlightRequests.completeLastSent(dest));
    }