public synchronized void addListen(String groupKey, String md5, String connectionId) {
        // 1.add groupKeyContext
        groupKeyContext.computeIfAbsent(groupKey, k -> new HashSet<>()).add(connectionId);
        // 2.add connectionIdContext
        connectionIdContext.computeIfAbsent(connectionId, k -> new HashMap<>(16)).put(groupKey, md5);
    }
@Test
    void testAddListen() {
        configChangeListenContext.addListen("groupKey", "md5", "connectionId");
        Set<String> groupKey = configChangeListenContext.getListeners("groupKey");
        assertEquals(1, groupKey.size());
    }