}

    @Override
    public WaitPrecondition getWaitPrecondition() {
        return this;
    }

    @Override
    public void assertCanWait() throws IllegalStateException {
        lock.lock();
        try {
            previous.assertCanWait();
            if (notReceived.isEmpty()) {
                // Have received all requests so downstream can wait.
                return;
            }

            httpExchange.sendResponseHeaders(200, 0);
        }
    }

    private class MustBeRunning implements WaitPrecondition {
        @Override
        public void assertCanWait() throws IllegalStateException {
            lock.lock();
            try {
                if (!running) {
                    throw new IllegalStateException("Cannot wait as the server is not running.");