add NoopSensor

Author: m-nagarajan

gradle.properties

@@ -1,6 +1,6 @@
 group=io.tehuti
 archivesBaseName=tehuti
-version=0.12.4
+version=0.12.5
 
 signing.enabled=false
 signing.keyId=

src/main/java/io/tehuti/metrics/MetricsRepository.java

@@ -142,6 +142,13 @@ public synchronized Sensor sensor(String name, MetricConfig config, Sensor... pa
         return s;
     }
 
+    /**
+     * Create a {@link NoopSensor} with the given name.
+     */
+    public Sensor getNoopSensor(String name) {
+        return new NoopSensor(this, name, null, this.config, time);
+    }
+
     /**
      * Remove a sensor with the given unique name. Unregister all metrics with this sensor too.
      * @param name The name of the sensor

src/main/java/io/tehuti/metrics/NoopSensor.java

@@ -0,0 +1,53 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE
+ * file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file
+ * to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the
+ * License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package io.tehuti.metrics;
+
+import io.tehuti.Metric;
+import io.tehuti.utils.Time;
+import java.util.Collections;
+import java.util.Map;
+
+
+/**
+ * A sensor that does nothing.
+ */
+public class NoopSensor extends Sensor {
+    NoopSensor(MetricsRepository registry, String name, Sensor[] parents, MetricConfig config, Time time) {
+        super(registry, name, parents, config, time);
+    }
+
+    @Override
+    public void record() {
+        // NOOP
+    }
+
+    @Override
+    public void record(double value) {
+        // NOOP
+    }
+
+    @Override
+    public void record(double value, long timeMs) {
+       //NOOP
+    }
+
+    @Override
+    public Map<String, Metric> add(CompoundStat stat, MetricConfig config) {
+        return Collections.emptyMap();
+    }
+
+    @Override
+    public Metric add(String name, String description, MeasurableStat stat, MetricConfig config) {
+        return null;
+    }
+}

src/test/java/io/tehuti/metrics/stats/NoopSensorTest.java

@@ -0,0 +1,81 @@
+package io.tehuti.metrics.stats;
+
+import io.tehuti.Metric;
+import io.tehuti.metrics.JmxReporter;
+import io.tehuti.metrics.MetricConfig;
+import io.tehuti.metrics.MetricsReporter;
+import io.tehuti.metrics.MetricsRepository;
+import io.tehuti.metrics.Sensor;
+import io.tehuti.utils.MockTime;
+import java.util.Arrays;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Unit tests for {@link io.tehuti.metrics.NoopSensor}.
+ */
+public class NoopSensorTest {
+
+    @Test
+    public void testNoopSensorIsNotRegisteredAndHasName() {
+        MockTime time = new MockTime();
+        MetricConfig config = new MetricConfig();
+        MetricsRepository repo = new MetricsRepository(config, Arrays.asList((MetricsReporter) new JmxReporter()), time);
+
+        Sensor noop = repo.getNoopSensor("noop");
+
+        // Name should be set
+        assertEquals("noop", noop.name());
+        // NoopSensor is not tracked/registered in the repository
+        assertNull(repo.getSensor("noop"));
+        // Repository should have no metrics
+        assertTrue(repo.metrics().isEmpty());
+    }
+
+    @Test
+    public void testRecordDoesNothing() {
+        MockTime time = new MockTime();
+        MetricConfig config = new MetricConfig();
+        MetricsRepository repo = new MetricsRepository(config, Arrays.asList((MetricsReporter) new JmxReporter()), time);
+
+        Sensor noop = repo.getNoopSensor("noop");
+
+        // Invoke all record variants; should be no-ops and not throw
+        noop.record();
+        noop.record(1.23);
+        noop.record(4.56, time.milliseconds());
+
+        // Still no metrics registered/affected
+        assertTrue(repo.metrics().isEmpty());
+    }
+
+    @Test
+    public void testAddMethodsReturnNullOrEmptyAndDoNotRegisterMetrics() {
+        MockTime time = new MockTime();
+        MetricConfig config = new MetricConfig();
+        MetricsRepository repo = new MetricsRepository(config, Arrays.asList((MetricsReporter) new JmxReporter()), time);
+
+        Sensor noop = repo.getNoopSensor("noop");
+
+        // MeasurableStat adds should return null and not register metrics
+        Metric m1 = noop.add("test.avg", new Avg());
+        Metric m2 = noop.add("test.avg2", "desc", new Avg());
+        Metric m3 = noop.add("test.avg3", new Avg(), new MetricConfig());
+        assertNull(m1);
+        assertNull(m2);
+        assertNull(m3);
+
+        // CompoundStat adds should return empty map and not register metrics
+        Percentiles percs = new Percentiles(10, 0.0, 100.0, Percentiles.BucketSizing.CONSTANT,
+            new Percentile("noop.p50", 50.0));
+        assertTrue(noop.add(percs, null).isEmpty());
+
+        // Repository should still have no metrics registered
+        assertTrue(repo.metrics().isEmpty());
+        assertNull(repo.getMetric("test.avg"));
+        assertNull(repo.getMetric("noop.p50"));
+    }
+}