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