### Question:
ProxyServers { public static boolean isProxyServer(String remoteAddr) { if (proxyServers == null) { refresh(); } return proxyServers.contains(remoteAddr); }  static void refresh(); static void refresh(Configuration conf); static boolean isProxyServer(String remoteAddr); static final String CONF_HADOOP_PROXYSERVERS; }### Answer:
@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")); }