@Test
public void testProxyServer() {

  Configuration conf = new Configuration();
  assertFalse(ProxyServers.isProxyServer("1.1.1.1"));
  conf.set(ProxyServers.CONF_HADOOP_PROXYSERVERS, "2.2.2.2, 3.3.3.3");
  ProxyUsers.refreshSuperUserGroupsConfiguration(conf);
  assertFalse(ProxyServers.isProxyServer("1.1.1.1"));
  assertTrue(ProxyServers.isProxyServer("2.2.2.2"));
  assertTrue(ProxyServers.isProxyServer("3.3.3.3"));
}