public static ConnectionGroup getOrCreateGroup(String namespace) {
        AssertUtil.assertNotBlank(namespace, "namespace should not be empty");
        ConnectionGroup group = CONN_MAP.get(namespace);
        if (group == null) {
            synchronized (CREATE_LOCK) {
                if ((group = CONN_MAP.get(namespace)) == null) {
                    group = new ConnectionGroup(namespace);
                    CONN_MAP.put(namespace, group);
                }
            }
        }
        return group;
    }
@Test(expected = IllegalArgumentException.class)
    public void testGetOrCreateGroupBadNamespace() {
        ConnectionManager.getOrCreateGroup("");
    }