Adding NullStatsReporter and TestScope

core/src/main/java/com/uber/m3/tally/NullStatsReporter.java

@@ -0,0 +1,83 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package com.uber.m3.tally;
+
+import com.uber.m3.util.Duration;
+
+import java.util.Map;
+
+/**
+ * NullStatsReporter is a noop implementation of StatsReporter.
+ */
+public class NullStatsReporter implements StatsReporter {
+    @Override
+    public void reportCounter(String name, Map<String, String> tags, long value) {
+        // noop
+    }
+
+    @Override
+    public void reportGauge(String name, Map<String, String> tags, double value) {
+        // noop
+    }
+
+    @Override
+    public void reportTimer(String name, Map<String, String> tags, Duration interval) {
+        // noop
+    }
+
+    @Override
+    public void reportHistogramValueSamples(
+        String name, Map<String,
+        String> tags,
+        Buckets buckets,
+        double bucketLowerBound,
+        double bucketUpperBound,
+        long samples
+    ) {
+        // noop
+    }
+
+    @Override
+    public void reportHistogramDurationSamples(
+        String name,
+        Map<String, String> tags,
+        Buckets buckets,
+        Duration bucketLowerBound,
+        Duration bucketUpperBound, long samples
+    ) {
+        // noop
+    }
+
+    @Override
+    public Capabilities capabilities() {
+        return CapableOf.NONE;
+    }
+
+    @Override
+    public void flush() {
+        // noop
+    }
+
+    @Override
+    public void close() {
+        // noop
+    }
+}

core/src/main/java/com/uber/m3/tally/ScopeBuilder.java

@@ -144,22 +144,29 @@ public Scope reportEvery(Duration interval) {
     }
 
     /**
-     * Creates a root scope and starts reporting with the specified interval
+     * Creates a root scope and starts reporting with the specified interval.
+     * No reporting is done for the {@link NullStatsReporter}.
      * @param interval duration between each report
      * @param uncaughtExceptionHandler an  {@link java.lang.Thread.UncaughtExceptionHandler} that's
      *                                 called when there's an uncaught exception in the report loop
      * @return the root scope created
      */
-    public Scope reportEvery(Duration interval,
-                             Thread.UncaughtExceptionHandler uncaughtExceptionHandler) {
-        if (interval.compareTo(Duration.ZERO) <= 0) {
-            throw new IllegalArgumentException("Reporting interval must be a positive Duration");
+    public Scope reportEvery(
+        Duration interval,
+        Thread.UncaughtExceptionHandler uncaughtExceptionHandler
+    ) {
+        if (reporter instanceof NullStatsReporter) {
+            interval = Duration.ZERO;
+        } else if (interval.compareTo(Duration.ZERO) <= 0) {
+            throw new IllegalArgumentException("Reporting interval must be a non-negative Duration");
         }
 
         ScopeImpl scope = build();
         registry.subscopes.put(ScopeImpl.keyForPrefixedStringMap(prefix, tags), scope);
 
-        scheduler.scheduleWithFixedDelay(scope.new ReportLoop(uncaughtExceptionHandler), 0, interval.toMillis(), TimeUnit.MILLISECONDS);
+        if (interval.compareTo(Duration.ZERO) > 0) {
+            scheduler.scheduleWithFixedDelay(scope.new ReportLoop(uncaughtExceptionHandler), 0, interval.toMillis(), TimeUnit.MILLISECONDS);
+        }
 
         return scope;
     }

core/src/main/java/com/uber/m3/tally/ScopeImpl.java

@@ -32,7 +32,7 @@
 /**
  * Default {@link Scope} implementation.
  */
-class ScopeImpl implements Scope {
+class ScopeImpl implements Scope, TestScope {
     private StatsReporter reporter;
     private String prefix;
     private String separator;
@@ -244,6 +244,7 @@ String fullyQualifiedName(String name) {
      * Returns a {@link Snapshot} of this {@link Scope}.
      * @return a {@link Snapshot} of this {@link Scope}
      */
+    @Override
     public Snapshot snapshot() {
         Snapshot snap = new SnapshotImpl();
 

core/src/main/java/com/uber/m3/tally/TestScope.java

@@ -0,0 +1,60 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package com.uber.m3.tally;
+
+import com.uber.m3.util.Duration;
+
+import java.util.Map;
+
+/**
+ * TestScope is a metrics collector that has no reporting, ensuring that
+ * all emitted values have a given prefix or set of tags.
+ */
+interface TestScope extends Scope {
+
+    /**
+     * Creates a new TestScope that adds the ability to take snapshots of
+     * metrics emitted to it.
+     */
+    static TestScope create() {
+        return (TestScope) new RootScopeBuilder()
+            .reporter(new NullStatsReporter())
+            .reportEvery(Duration.ZERO);
+    }
+
+    /**
+     * Creates a new TestScope with given prefix/tags that adds the ability to
+     * take snapshots of metrics emitted to it.
+     */
+    static TestScope create(String prefix, Map<String, String> tags) {
+        return (TestScope) new RootScopeBuilder()
+            .prefix(prefix)
+            .tags(tags)
+            .reporter(new NullStatsReporter())
+            .reportEvery(Duration.ZERO);
+    }
+
+    /**
+     * Snapshot returns a copy of all values since the last report execution
+     * This is an expensive operation and should only be used for testing purposes.
+     */
+    Snapshot snapshot();
+}

core/src/test/java/com/uber/m3/tally/NullStatsReporterTest.java

@@ -0,0 +1,37 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package com.uber.m3.tally;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+
+public class NullStatsReporterTest {
+
+    @Test
+    public void capabilities() {
+        NullStatsReporter reporter = new NullStatsReporter();
+        assertNotNull(reporter.capabilities());
+        assertFalse(reporter.capabilities().reporting());
+        assertFalse(reporter.capabilities().tagging());
+    }
+}