private void sleep() throws InterruptedException {
        final long delay = assertTimeoutPreemptively(ofSeconds(1), () -> this.delays.take());
        if (delay <= 0) {
            throw new IllegalStateException("Bad delay: " + delay);
        }
        Thread.sleep(delay);
    }
Waits until all request have started processing on the server.
tests/src/test/java/net/devh/boot/grpc/test/server/WaitingTestService.java