Adding TestScope interface and factory method

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/ScopeImplTest.java

@@ -217,7 +217,7 @@ public void snapshot() {
             System.err.println("Interrupted while sleeping! Let's continue anyway...");
         }
 
-        Snapshot snapshot = ((ScopeImpl) rootScope).snapshot();
+        Snapshot snapshot = ((TestScope) rootScope).snapshot();
 
         Map<String, CounterSnapshot> counters = snapshot.counters();
         assertEquals(1, counters.size());

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

@@ -0,0 +1,65 @@
+// 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.ImmutableMap;
+import org.junit.Test;
+
+import java.util.Map;
+
+import static org.hamcrest.CoreMatchers.instanceOf;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertThat;
+
+public class TestScopeTest {
+
+    @Test
+    public void getInstance() {
+        TestScope testScope = TestScope.create();
+        assertNotNull(testScope);
+        assertThat(testScope, instanceOf(Scope.class));
+        assertThat(testScope, instanceOf(ScopeImpl.class));
+
+        assertNotNull(testScope.capabilities());
+        assertFalse(testScope.capabilities().reporting());
+        assertFalse(testScope.capabilities().tagging());
+    }
+
+    @Test
+    public void prefixTags() {
+        Map<String, String> tags = ImmutableMap.of("key", "value");
+        TestScope testScope = TestScope.create("prefix", tags);
+        testScope.counter("counter").inc(1);
+
+        Snapshot snapshot = testScope.snapshot();
+        assertNotNull(snapshot);
+
+        Map<String, CounterSnapshot> counters = snapshot.counters();
+        assertNotNull(counters);
+        assertEquals(1, counters.size());
+        assertNotNull(counters.get("prefix.counter+key=value"));
+        assertEquals("prefix.counter", counters.get("prefix.counter+key=value").name());
+        assertEquals(tags, counters.get("prefix.counter+key=value").tags());
+        assertEquals(1, counters.get("prefix.counter+key=value").value());
+    }
+}