Plugs-in the LongGauge into the registry (#1498)

* plug-in longGauge into MetricRegistry

* Minor fix

* Add TODO and Fix build

* Fix review comments

6 files changed, 134 insertions, 499 deletions

diff --git a/api/src/main/java/io/opencensus/metrics/DoubleGauge.java b/api/src/main/java/io/opencensus/metrics/DoubleGauge.java
index 91e131ec..62730a06 100644
--- a/api/src/main/java/io/opencensus/metrics/DoubleGauge.java
+++ b/api/src/main/java/io/opencensus/metrics/DoubleGauge.java
@@ -86,12 +86,12 @@ public abstract class DoubleGauge {
    * method for manual operations.
    *
    * @param labelValues the list of label values. The number of label values must be the same to
-   *     that of the label keys passed to {@link MetricRegistry#addDoubleGauge}.
+   *     that of the label keys.
    * @return a {@code DoublePoint} the value of single gauge.
    * @throws NullPointerException if {@code labelValues} is null OR any element of {@code
    *     labelValues} is null.
    * @throws IllegalArgumentException if number of {@code labelValues}s are not equal to the label
-   *     keys passed to {@link MetricRegistry#addDoubleGauge}.
+   *     keys.
    * @since 0.17
    */
   public abstract DoublePoint getOrCreateTimeSeries(List<LabelValue> labelValues);
diff --git a/api/src/main/java/io/opencensus/metrics/LongGauge.java b/api/src/main/java/io/opencensus/metrics/LongGauge.java
index 42951d50..f473a8ac 100644
--- a/api/src/main/java/io/opencensus/metrics/LongGauge.java
+++ b/api/src/main/java/io/opencensus/metrics/LongGauge.java
@@ -32,7 +32,7 @@ import javax.annotation.concurrent.ThreadSafe;
  *   private static final MetricRegistry metricRegistry = Metrics.getMetricRegistry();
  *
  *   List<LabelKey> labelKeys = Arrays.asList(LabelKey.create("Name", "desc"));
- *   // TODO(mayurkale): Plugs-in the LongGauge into the registry.
+ *
  *   LongGauge gauge = metricRegistry.addLongGauge("queue_size", "Pending jobs", "1", labelKeys);
  *
  *   // It is recommended to keep a reference of a point for manual operations.
@@ -56,7 +56,6 @@ import javax.annotation.concurrent.ThreadSafe;
  *   List<LabelKey> labelKeys = Arrays.asList(LabelKey.create("Name", "desc"));
  *   List<LabelValue> labelValues = Arrays.asList(LabelValue.create("Inbound"));
  *
- *   // TODO(mayurkale): Plugs-in the LongGauge into the registry.
  *   LongGauge gauge = metricRegistry.addLongGauge("queue_size", "Pending jobs", "1", labelKeys);
  *
  *   // It is recommended to keep a reference of a point for manual operations.
@@ -167,11 +166,6 @@ public abstract class LongGauge {
 
     /** Creates a new {@code NoopLongPoint}. */
     NoopLongGauge(String name, String description, String unit, List<LabelKey> labelKeys) {
-      Utils.checkNotNull(name, "name");
-      Utils.checkNotNull(description, "description");
-      Utils.checkNotNull(unit, "unit");
-      Utils.checkNotNull(labelKeys, "labelKeys should not be null.");
-      Utils.checkListElementNotNull(labelKeys, "labelKeys element should not be null.");
       labelKeysSize = labelKeys.size();
     }
 
diff --git a/api/src/main/java/io/opencensus/metrics/MetricRegistry.java b/api/src/main/java/io/opencensus/metrics/MetricRegistry.java
index a9987b75..840ad787 100644
--- a/api/src/main/java/io/opencensus/metrics/MetricRegistry.java
+++ b/api/src/main/java/io/opencensus/metrics/MetricRegistry.java
@@ -17,10 +17,8 @@
 package io.opencensus.metrics;
 
 import io.opencensus.common.ExperimentalApi;
-import io.opencensus.common.ToDoubleFunction;
-import io.opencensus.common.ToLongFunction;
 import io.opencensus.internal.Utils;
-import java.util.LinkedHashMap;
+import java.util.List;
 
 /**
  * Creates and manages your application's set of metrics. The default implementation of this creates
@@ -32,44 +30,21 @@ import java.util.LinkedHashMap;
 @ExperimentalApi
 public abstract class MetricRegistry {
   /**
-   * Build a new long gauge to be added to the registry.
-   *
-   * <p>Must be called only once.
+   * Builds a new long gauge to be added to the registry. This is more convenient form when you want
+   * to manually increase and decrease values as per your service requirements.
    *
    * @param name the name of the metric.
    * @param description the description of the metric.
    * @param unit the unit of the metric.
-   * @param obj the function argument.
-   * @param function the function to be called.
+   * @param labelKeys the list of the label keys.
+   * @throws NullPointerException if {@code labelKeys} is null OR any element of {@code labelKeys}
+   *     is null OR {@code name}, {@code description}, {@code unit} is null.
+   * @throws IllegalArgumentException if different metric with the same name already registered.
    * @since 0.17
    */
-  public abstract <T> void addLongGauge(
-      String name,
-      String description,
-      String unit,
-      LinkedHashMap<LabelKey, LabelValue> labels,
-      T obj,
-      ToLongFunction<T> function);
-
-  /**
-   * Build a new double gauge to be added to the registry.
-   *
-   * <p>Must be called only once.
-   *
-   * @param name the name of the metric.
-   * @param description the description of the metric.
-   * @param unit the unit of the metric.
-   * @param obj the function argument.
-   * @param function the function to be called.
-   * @since 0.17
-   */
-  public abstract <T> void addDoubleGauge(
-      String name,
-      String description,
-      String unit,
-      LinkedHashMap<LabelKey, LabelValue> labels,
-      T obj,
-      ToDoubleFunction<T> function);
+  @ExperimentalApi
+  public abstract LongGauge addLongGauge(
+      String name, String description, String unit, List<LabelKey> labelKeys);
 
   static MetricRegistry newNoopMetricRegistry() {
     return new NoopMetricRegistry();
@@ -78,33 +53,15 @@ public abstract class MetricRegistry {
   private static final class NoopMetricRegistry extends MetricRegistry {
 
     @Override
-    public <T> void addLongGauge(
-        String name,
-        String description,
-        String unit,
-        LinkedHashMap<LabelKey, LabelValue> labels,
-        T obj,
-        ToLongFunction<T> function) {
-      Utils.checkNotNull(name, "name");
-      Utils.checkNotNull(description, "description");
-      Utils.checkNotNull(unit, "unit");
-      Utils.checkNotNull(labels, "labels");
-      Utils.checkNotNull(function, "function");
-    }
-
-    @Override
-    public <T> void addDoubleGauge(
-        String name,
-        String description,
-        String unit,
-        LinkedHashMap<LabelKey, LabelValue> labels,
-        T obj,
-        ToDoubleFunction<T> function) {
-      Utils.checkNotNull(name, "name");
-      Utils.checkNotNull(description, "description");
-      Utils.checkNotNull(unit, "unit");
-      Utils.checkNotNull(labels, "labels");
-      Utils.checkNotNull(function, "function");
+    public LongGauge addLongGauge(
+        String name, String description, String unit, List<LabelKey> labelKeys) {
+      Utils.checkListElementNotNull(
+          Utils.checkNotNull(labelKeys, "labelKeys"), "labelKey element should not be null.");
+      return LongGauge.newNoopLongGauge(
+          Utils.checkNotNull(name, "name"),
+          Utils.checkNotNull(description, "description"),
+          Utils.checkNotNull(unit, "unit"),
+          labelKeys);
     }
   }
 }
diff --git a/api/src/test/java/io/opencensus/metrics/MetricRegistryTest.java b/api/src/test/java/io/opencensus/metrics/MetricRegistryTest.java
index 49e8ce02..0d90fa97 100644
--- a/api/src/test/java/io/opencensus/metrics/MetricRegistryTest.java
+++ b/api/src/test/java/io/opencensus/metrics/MetricRegistryTest.java
@@ -16,9 +16,10 @@
 
 package io.opencensus.metrics;
 
-import io.opencensus.common.ToDoubleFunction;
-import io.opencensus.common.ToLongFunction;
-import java.util.LinkedHashMap;
+import static com.google.common.truth.Truth.assertThat;
+
+import java.util.Collections;
+import java.util.List;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
@@ -30,156 +31,64 @@ import org.junit.runners.JUnit4;
 public class MetricRegistryTest {
   @Rule public ExpectedException thrown = ExpectedException.none();
 
+  private static final String NAME = "name";
+  private static final String DESCRIPTION = "description";
+  private static final String UNIT = "1";
+  private static final List<LabelKey> LABEL_KEY =
+      Collections.singletonList(LabelKey.create("key", "key description"));
+  private static final List<LabelValue> LABEL_VALUES =
+      Collections.singletonList(LabelValue.create("value"));
   private final MetricRegistry metricRegistry =
       MetricsComponent.newNoopMetricsComponent().getMetricRegistry();
 
   @Test
-  public void addDoubleGauge_NullName() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        null,
-        "description",
-        "1",
-        new LinkedHashMap<LabelKey, LabelValue>(),
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
-  }
-
-  @Test
-  public void addDoubleGauge_NullDescription() {
+  public void noopAddLongGauge_NullName() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        "name",
-        null,
-        "1",
-        new LinkedHashMap<LabelKey, LabelValue>(),
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
+    thrown.expectMessage("name");
+    metricRegistry.addLongGauge(null, DESCRIPTION, UNIT, LABEL_KEY);
   }
 
   @Test
-  public void addDoubleGauge_NullUnit() {
+  public void noopAddLongGauge_NullDescription() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        "name",
-        "description",
-        null,
-        new LinkedHashMap<LabelKey, LabelValue>(),
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
+    thrown.expectMessage("description");
+    metricRegistry.addLongGauge(NAME, null, UNIT, LABEL_KEY);
   }
 
   @Test
-  public void addDoubleGauge_NullLabels() {
+  public void noopAddLongGauge_NullUnit() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        "name",
-        "description",
-        "1",
-        null,
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
+    thrown.expectMessage("unit");
+    metricRegistry.addLongGauge(NAME, DESCRIPTION, null, LABEL_KEY);
   }
 
   @Test
-  public void addDoubleGauge_NullFunction() {
+  public void noopAddLongGauge_NullLabels() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        "name", "description", "1", new LinkedHashMap<LabelKey, LabelValue>(), null, null);
+    thrown.expectMessage("labelKeys");
+    metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, null);
   }
 
   @Test
-  public void addLongGauge_NullName() {
+  public void noopAddLongGauge_WithNullElement() {
+    List<LabelKey> labelKeys = Collections.singletonList(null);
     thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        null,
-        "description",
-        "1",
-        new LinkedHashMap<LabelKey, LabelValue>(),
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 5;
-          }
-        });
+    thrown.expectMessage("labelKey element should not be null.");
+    metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, labelKeys);
   }
 
   @Test
-  public void addLongGauge_NullDescription() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        "name",
-        null,
-        "1",
-        new LinkedHashMap<LabelKey, LabelValue>(),
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 5;
-          }
-        });
+  public void noopSameAs() {
+    LongGauge longGauge = metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    assertThat(longGauge.getDefaultTimeSeries()).isSameAs(longGauge.getDefaultTimeSeries());
+    assertThat(longGauge.getDefaultTimeSeries())
+        .isSameAs(longGauge.getOrCreateTimeSeries(LABEL_VALUES));
   }
 
   @Test
-  public void addLongGauge_NullUnit() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        "name",
-        "description",
-        null,
-        new LinkedHashMap<LabelKey, LabelValue>(),
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 5;
-          }
-        });
-  }
-
-  @Test
-  public void addLongGauge_NullLabels() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        "name",
-        "description",
-        "1",
-        null,
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 5;
-          }
-        });
-  }
-
-  @Test
-  public void addLongGauge_NullFunction() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        "name", "description", "1", new LinkedHashMap<LabelKey, LabelValue>(), null, null);
+  public void noopInstanceOf() {
+    LongGauge longGauge = metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    assertThat(longGauge)
+        .isInstanceOf(LongGauge.newNoopLongGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY).getClass());
   }
 }
diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java
index 3a30fd38..8f8dab2b 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java
@@ -19,12 +19,9 @@ package io.opencensus.implcore.metrics;
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import io.opencensus.common.Clock;
-import io.opencensus.common.ToDoubleFunction;
-import io.opencensus.common.ToLongFunction;
-import io.opencensus.implcore.metrics.Gauge.DoubleGauge;
-import io.opencensus.implcore.metrics.Gauge.LongGauge;
+import io.opencensus.implcore.internal.Utils;
 import io.opencensus.metrics.LabelKey;
-import io.opencensus.metrics.LabelValue;
+import io.opencensus.metrics.LongGauge;
 import io.opencensus.metrics.MetricRegistry;
 import io.opencensus.metrics.export.Metric;
 import io.opencensus.metrics.export.MetricProducer;
@@ -32,8 +29,8 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
-import java.util.LinkedHashSet;
-import java.util.Set;
+import java.util.List;
+import java.util.Map;
 
 /** Implementation of {@link MetricRegistry}. */
 public final class MetricRegistryImpl extends MetricRegistry {
@@ -46,56 +43,38 @@ public final class MetricRegistryImpl extends MetricRegistry {
   }
 
   @Override
-  public <T> void addLongGauge(
-      String name,
-      String description,
-      String unit,
-      LinkedHashMap<LabelKey, LabelValue> labels,
-      T obj,
-      ToLongFunction<T> function) {
-    checkNotNull(labels, "labels");
-    registeredMeters.registerMeter(
-        new LongGauge<T>(
+  public LongGauge addLongGauge(
+      String name, String description, String unit, List<LabelKey> labelKeys) {
+    Utils.checkListElementNotNull(
+        checkNotNull(labelKeys, "labelKeys"), "labelKey element should not be null.");
+    LongGaugeImpl longGaugeMetric =
+        new LongGaugeImpl(
             checkNotNull(name, "name"),
             checkNotNull(description, "description"),
             checkNotNull(unit, "unit"),
-            Collections.unmodifiableList(new ArrayList<LabelKey>(labels.keySet())),
-            Collections.unmodifiableList(new ArrayList<LabelValue>(labels.values())),
-            obj,
-            checkNotNull(function, "function")));
-  }
-
-  @Override
-  public <T> void addDoubleGauge(
-      String name,
-      String description,
-      String unit,
-      LinkedHashMap<LabelKey, LabelValue> labels,
-      T obj,
-      ToDoubleFunction<T> function) {
-    checkNotNull(labels, "labels");
-    registeredMeters.registerMeter(
-        new DoubleGauge<T>(
-            checkNotNull(name, "name"),
-            checkNotNull(description, "description"),
-            checkNotNull(unit, "unit"),
-            Collections.unmodifiableList(new ArrayList<LabelKey>(labels.keySet())),
-            Collections.unmodifiableList(new ArrayList<LabelValue>(labels.values())),
-            obj,
-            checkNotNull(function, "function")));
+            Collections.unmodifiableList(new ArrayList<LabelKey>(labelKeys)));
+    registeredMeters.registerMeter(name, longGaugeMetric);
+    return longGaugeMetric;
   }
 
   private static final class RegisteredMeters {
-    private volatile Set<Gauge> registeredGauges = Collections.emptySet();
+    private volatile Map<String, Meter> registeredMeters = Collections.emptyMap();
 
-    private Set<Gauge> getRegisteredMeters() {
-      return registeredGauges;
+    private Map<String, Meter> getRegisteredMeters() {
+      return registeredMeters;
     }
 
-    private synchronized void registerMeter(Gauge gauge) {
-      Set<Gauge> newGaguesList = new LinkedHashSet<Gauge>(registeredGauges);
-      newGaguesList.add(gauge);
-      registeredGauges = Collections.unmodifiableSet(newGaguesList);
+    private synchronized void registerMeter(String meterName, Meter meter) {
+      Meter existingMeter = registeredMeters.get(meterName);
+      if (existingMeter != null) {
+        // TODO(mayurkale): Allow users to register the same Meter multiple times without exception.
+        throw new IllegalArgumentException(
+            "A different metric with the same name already registered.");
+      }
+
+      Map<String, Meter> registeredMetersCopy = new LinkedHashMap<String, Meter>(registeredMeters);
+      registeredMetersCopy.put(meterName, meter);
+      registeredMeters = Collections.unmodifiableMap(registeredMetersCopy);
     }
   }
 
@@ -110,14 +89,18 @@ public final class MetricRegistryImpl extends MetricRegistry {
 
     @Override
     public Collection<Metric> getMetrics() {
-      // Get a snapshot of the current registered gauges.
-      Set<Gauge> gaguges = registeredMeters.getRegisteredMeters();
-      if (gaguges.isEmpty()) {
+      // Get a snapshot of the current registered meters.
+      Map<String, Meter> meters = registeredMeters.getRegisteredMeters();
+      if (meters.isEmpty()) {
         return Collections.emptyList();
       }
-      ArrayList<Metric> metrics = new ArrayList<Metric>();
-      for (Gauge gauge : gaguges) {
-        metrics.add(gauge.getMetric(clock));
+
+      List<Metric> metrics = new ArrayList<Metric>(meters.size());
+      for (Map.Entry<String, Meter> entry : meters.entrySet()) {
+        Metric metric = entry.getValue().getMetric(clock);
+        if (metric != null) {
+          metrics.add(metric);
+        }
       }
       return metrics;
     }
diff --git a/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java b/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java
index 5210b266..c7cd99be 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java
@@ -19,10 +19,9 @@ package io.opencensus.implcore.metrics;
 import static com.google.common.truth.Truth.assertThat;
 
 import io.opencensus.common.Timestamp;
-import io.opencensus.common.ToDoubleFunction;
-import io.opencensus.common.ToLongFunction;
 import io.opencensus.metrics.LabelKey;
 import io.opencensus.metrics.LabelValue;
+import io.opencensus.metrics.LongGauge;
 import io.opencensus.metrics.export.Metric;
 import io.opencensus.metrics.export.MetricDescriptor;
 import io.opencensus.metrics.export.MetricDescriptor.Type;
@@ -30,9 +29,9 @@ import io.opencensus.metrics.export.Point;
 import io.opencensus.metrics.export.TimeSeries;
 import io.opencensus.metrics.export.Value;
 import io.opencensus.testing.common.TestClock;
+import java.util.Collection;
 import java.util.Collections;
-import java.util.LinkedHashMap;
-import org.junit.Before;
+import java.util.List;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
@@ -42,289 +41,82 @@ import org.junit.runners.JUnit4;
 /** Unit tests for {@link MetricRegistryImpl}. */
 @RunWith(JUnit4.class)
 public class MetricRegistryImplTest {
+  @Rule public ExpectedException thrown = ExpectedException.none();
+
   private static final String NAME = "name";
   private static final String DESCRIPTION = "description";
   private static final String UNIT = "1";
-  private static final LabelKey LABEL_KEY = LabelKey.create("key", "key description");
-  private static final LabelValue LABEL_VALUES = LabelValue.create("value");
-  private static final Timestamp TEST_TIME = Timestamp.create(1234, 123);
-
-  @Rule public ExpectedException thrown = ExpectedException.none();
+  private static final List<LabelKey> LABEL_KEY =
+      Collections.singletonList(LabelKey.create("key", "key description"));
+  private static final List<LabelValue> LABEL_VALUES =
+      Collections.singletonList(LabelValue.create("value"));
 
+  private static final Timestamp TEST_TIME = Timestamp.create(1234, 123);
   private final TestClock testClock = TestClock.create(TEST_TIME);
   private final MetricRegistryImpl metricRegistry = new MetricRegistryImpl(testClock);
-  private final LinkedHashMap<LabelKey, LabelValue> labels =
-      new LinkedHashMap<LabelKey, LabelValue>();
-
-  @Before
-  public void setUp() {
-    labels.put(LABEL_KEY, LABEL_VALUES);
-  }
 
-  @Test
-  public void addDoubleGauge_NullName() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        null,
-        DESCRIPTION,
-        UNIT,
-        labels,
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
-  }
-
-  @Test
-  public void addDoubleGauge_NullDescription() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        NAME,
-        null,
-        UNIT,
-        labels,
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
-  }
-
-  @Test
-  public void addDoubleGauge_NullUnit() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        NAME,
-        DESCRIPTION,
-        null,
-        labels,
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
-  }
-
-  @Test
-  public void addDoubleGauge_NullLabels() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(
-        NAME,
-        DESCRIPTION,
-        UNIT,
-        null,
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
-  }
-
-  @Test
-  public void addDoubleGauge_NullFunction() {
-    thrown.expect(NullPointerException.class);
-    metricRegistry.addDoubleGauge(NAME, DESCRIPTION, UNIT, labels, null, null);
-  }
-
-  @Test
-  public void addDoubleGauge_GetMetrics() {
-    metricRegistry.addDoubleGauge(
-        NAME,
-        DESCRIPTION,
-        UNIT,
-        labels,
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
-    assertThat(metricRegistry.getMetricProducer().getMetrics())
-        .containsExactly(
-            Metric.create(
-                MetricDescriptor.create(
-                    NAME,
-                    DESCRIPTION,
-                    UNIT,
-                    Type.GAUGE_DOUBLE,
-                    Collections.unmodifiableList(Collections.singletonList(LABEL_KEY))),
-                Collections.singletonList(
-                    TimeSeries.createWithOnePoint(
-                        Collections.unmodifiableList(Collections.singletonList(LABEL_VALUES)),
-                        Point.create(Value.doubleValue(5.0), TEST_TIME),
-                        null))));
-  }
+  private static final MetricDescriptor METRIC_DESCRIPTOR =
+      MetricDescriptor.create(NAME, DESCRIPTION, UNIT, Type.GAUGE_INT64, LABEL_KEY);
 
   @Test
   public void addLongGauge_NullName() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        null,
-        DESCRIPTION,
-        UNIT,
-        labels,
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 7;
-          }
-        });
+    thrown.expectMessage("name");
+    metricRegistry.addLongGauge(null, DESCRIPTION, UNIT, LABEL_KEY);
   }
 
   @Test
   public void addLongGauge_NullDescription() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        NAME,
-        null,
-        UNIT,
-        labels,
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 5;
-          }
-        });
+    thrown.expectMessage("description");
+    metricRegistry.addLongGauge(NAME, null, UNIT, LABEL_KEY);
   }
 
   @Test
   public void addLongGauge_NullUnit() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        NAME,
-        DESCRIPTION,
-        null,
-        labels,
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 5;
-          }
-        });
+    thrown.expectMessage("unit");
+    metricRegistry.addLongGauge(NAME, DESCRIPTION, null, LABEL_KEY);
   }
 
   @Test
   public void addLongGauge_NullLabels() {
     thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge(
-        NAME,
-        DESCRIPTION,
-        UNIT,
-        null,
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 5;
-          }
-        });
+    thrown.expectMessage("labelKeys");
+    metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, null);
   }
 
   @Test
-  public void addLongGauge_NullFunction() {
+  public void addLongGauge_WithNullElement() {
+    List<LabelKey> labelKeys = Collections.singletonList(null);
     thrown.expect(NullPointerException.class);
-    metricRegistry.addLongGauge("name", DESCRIPTION, UNIT, labels, null, null);
+    thrown.expectMessage("labelKey element should not be null.");
+    metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, labelKeys);
   }
 
   @Test
   public void addLongGauge_GetMetrics() {
-    metricRegistry.addLongGauge(
-        NAME,
-        DESCRIPTION,
-        UNIT,
-        labels,
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 7;
-          }
-        });
-    assertThat(metricRegistry.getMetricProducer().getMetrics())
-        .containsExactly(
-            Metric.create(
-                MetricDescriptor.create(
-                    NAME,
-                    DESCRIPTION,
-                    UNIT,
-                    Type.GAUGE_INT64,
-                    Collections.unmodifiableList(Collections.singletonList(LABEL_KEY))),
-                Collections.singletonList(
-                    TimeSeries.createWithOnePoint(
-                        Collections.unmodifiableList(Collections.singletonList(LABEL_VALUES)),
-                        Point.create(Value.longValue(7), TEST_TIME),
-                        null))));
-  }
+    LongGauge longGauge = metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    longGauge.getOrCreateTimeSeries(LABEL_VALUES);
 
-  @Test
-  public void multipleMetrics_GetMetrics() {
-    metricRegistry.addLongGauge(
-        NAME,
-        DESCRIPTION,
-        UNIT,
-        labels,
-        null,
-        new ToLongFunction<Object>() {
-          @Override
-          public long applyAsLong(Object value) {
-            return 7;
-          }
-        });
-    metricRegistry.addDoubleGauge(
-        NAME,
-        DESCRIPTION,
-        UNIT,
-        labels,
-        null,
-        new ToDoubleFunction<Object>() {
-          @Override
-          public double applyAsDouble(Object value) {
-            return 5.0;
-          }
-        });
-    assertThat(metricRegistry.getMetricProducer().getMetrics())
+    Collection<Metric> metricCollections = metricRegistry.getMetricProducer().getMetrics();
+    assertThat(metricCollections.size()).isEqualTo(1);
+    assertThat(metricCollections)
         .containsExactly(
-            Metric.create(
-                MetricDescriptor.create(
-                    NAME,
-                    DESCRIPTION,
-                    UNIT,
-                    Type.GAUGE_INT64,
-                    Collections.unmodifiableList(Collections.singletonList(LABEL_KEY))),
-                Collections.singletonList(
-                    TimeSeries.createWithOnePoint(
-                        Collections.unmodifiableList(Collections.singletonList(LABEL_VALUES)),
-                        Point.create(Value.longValue(7), TEST_TIME),
-                        null))),
-            Metric.create(
-                MetricDescriptor.create(
-                    NAME,
-                    DESCRIPTION,
-                    UNIT,
-                    Type.GAUGE_DOUBLE,
-                    Collections.unmodifiableList(Collections.singletonList(LABEL_KEY))),
-                Collections.singletonList(
-                    TimeSeries.createWithOnePoint(
-                        Collections.unmodifiableList(Collections.singletonList(LABEL_VALUES)),
-                        Point.create(Value.doubleValue(5.0), TEST_TIME),
-                        null))));
+            Metric.createWithOneTimeSeries(
+                METRIC_DESCRIPTOR,
+                TimeSeries.createWithOnePoint(
+                    LABEL_VALUES, Point.create(Value.longValue(0), TEST_TIME), null)));
   }
 
   @Test
   public void empty_GetMetrics() {
     assertThat(metricRegistry.getMetricProducer().getMetrics()).isEmpty();
   }
+
+  @Test
+  public void checkInstanceOf() {
+    LongGauge longGauge = metricRegistry.addLongGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    assertThat(longGauge).isInstanceOf(LongGaugeImpl.class);
+  }
 }