1 files changed, 57 insertions, 0 deletions
diff --git a/container-disc/src/test/java/com/yahoo/container/jdisc/metric/GarbageCollectionMetricsTest.java b/container-disc/src/test/java/com/yahoo/container/jdisc/metric/GarbageCollectionMetricsTest.java
new file mode 100644
index 00000000000..61d8763b852
--- /dev/null
+++ b/container-disc/src/test/java/com/yahoo/container/jdisc/metric/GarbageCollectionMetricsTest.java
@@ -0,0 +1,57 @@
+package com.yahoo.container.jdisc.metric;
+
+import com.yahoo.jdisc.Metric;
+import com.yahoo.test.ManualClock;
+import org.junit.Test;
+
+import java.lang.management.ManagementFactory;
+import java.time.Duration;
+import java.util.LinkedList;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+/**
+ * @author ollivir
+ */
+public class GarbageCollectionMetricsTest {
+    @Test
+    public void gc_metrics_are_collected_in_a_sliding_window() {
+        ManualClock clock = new ManualClock();
+        Metric metric = mock(Metric.class);
+        int garbageCollectors = ManagementFactory.getGarbageCollectorMXBeans().size();
+
+        Duration interval = GarbageCollectionMetrics.REPORTING_INTERVAL;
+        GarbageCollectionMetrics garbageCollectionMetrics = new GarbageCollectionMetrics(clock);
+        assertThat(garbageCollectionMetrics.getGcStatistics().keySet().size(), is(garbageCollectors));
+
+        clock.advance(interval.minus(Duration.ofMillis(10)));
+        garbageCollectionMetrics.emitMetrics(metric);
+        assertWindowLengths(garbageCollectionMetrics, 2);
+
+        clock.advance(Duration.ofMillis(10));
+        garbageCollectionMetrics.emitMetrics(metric);
+        assertWindowLengths(garbageCollectionMetrics, 3);
+
+        clock.advance(Duration.ofMillis(10));
+        garbageCollectionMetrics.emitMetrics(metric);
+        assertWindowLengths(garbageCollectionMetrics, 3);
+
+        clock.advance(interval);
+        garbageCollectionMetrics.emitMetrics(metric);
+        assertWindowLengths(garbageCollectionMetrics, 2);
+
+        verify(metric, times(garbageCollectors * 4 * 2)).set(anyString(), any(), any());
+    }
+
+    private static void assertWindowLengths(GarbageCollectionMetrics gcm, int count) {
+        for(LinkedList<GarbageCollectionMetrics.GcStats> window: gcm.getGcStatistics().values()) {
+            assertThat(window.size(), is(count));
+        }
+    }
+}