### Question:
Metrics { public static Counter getOpenConnectionsCounter() { return getOrCreateCounter(MetricsConstants.OPEN_CONNECTIONS); } private  Metrics(Configuration conf); static synchronized Metrics initialize(Configuration conf); static MetricRegistry getRegistry(); static synchronized void shutdown(); static Counter getOrCreateCounter(String name); static Timer getOrCreateTimer(String name); static AtomicInteger getOrCreateGauge(String name); static Counter getOpenConnectionsCounter();  }### Answer:
@Test public void testJsonStructure() throws Exception { File jsonReportFile = File.createTempFile("TestMetrics", ".json"); String jsonFile = jsonReportFile.getAbsolutePath(); Configuration conf = MetastoreConf.newMetastoreConf(); MetastoreConf.setVar(conf, MetastoreConf.ConfVars.METRICS_REPORTERS, "json"); MetastoreConf.setVar(conf, MetastoreConf.ConfVars.METRICS_JSON_FILE_LOCATION, jsonFile); MetastoreConf.setTimeVar(conf, MetastoreConf.ConfVars.METRICS_JSON_FILE_INTERVAL, REPORT_INTERVAL, TimeUnit.SECONDS); initializeMetrics(conf); Counter openConnections = Metrics.getOpenConnectionsCounter(); openConnections.inc(); Thread.sleep(REPORT_INTERVAL * 1000 + REPORT_INTERVAL * 1000 / 2); String json = new String(MetricsTestUtils.getFileData(jsonFile, 200, 10)); MetricsTestUtils.verifyMetricsJson(json, MetricsTestUtils.GAUGE, "buffers.direct.capacity"); MetricsTestUtils.verifyMetricsJson(json, MetricsTestUtils.GAUGE, "memory.heap.used"); MetricsTestUtils.verifyMetricsJson(json, MetricsTestUtils.GAUGE, "threads.count"); MetricsTestUtils.verifyMetricsJson(json, MetricsTestUtils.GAUGE, "classLoading.loaded"); MetricsTestUtils.verifyMetricsJson(json, MetricsTestUtils.COUNTER, MetricsConstants.OPEN_CONNECTIONS, 1); }