public Reactor start() {
        if (!STATE.compareAndSet(Reactor.this, NEW, RUNNING)) {
            throw new IllegalStateException("Can't start reactor, invalid state:" + state);
        }
        startLatch.countDown();
        return this;
    }
@Test(expected = IllegalStateException.class)
    public void test_start_whenAlreadyStarted() {
        Reactor reactor = newReactor();
        reactor.start();

        reactor.start();
    }