Design and provide unit tests to cover more use cases.
List<URL> urls = new ArrayList<>();
        urls.add(url1);
        urls.add(url2);
        urls.add(url3);
        abstractRegistry.notify(null, listner1, urls);
        Assert.fail("notify url == null");
    }
    @Test(expected = IllegalArgumentException.class)
    public void testNotifyIfNotifyNull() {
        final AtomicReference<Boolean> notified = new AtomicReference<Boolean>(false);
        NotifyListener listner1 = urls -> notified.set(Boolean.TRUE);
        URL url1 = new URL("dubbo", "192.168.0.1", 2200, parametersConsumer);
        abstractRegistry.subscribe(url1, listner1);
        NotifyListener listner2 = urls -> notified.set(Boolean.TRUE);
        URL url2 = new URL("dubbo", "192.168.0.2", 2201, parametersConsumer);
        abstractRegistry.subscribe(url2, listner2);
        NotifyListener listner3 = urls -> notified.set(Boolean.TRUE);
        URL url3 = new URL("dubbo", "192.168.0.3", 2202, parametersConsumer);
        abstractRegistry.subscribe(url3, listner3);
        List<URL> urls = new ArrayList<>();
        urls.add(url1);
        urls.add(url2);
        urls.add(url3);
        abstractRegistry.notify(url1, null, urls);
        Assert.fail("notify listener == null");
    }
    /**
     * Test method for
     * {@link org.apache.dubbo.registry.support.AbstractRegistry#notify(URL, NotifyListener, List)}.
     *