Adding unit test for test isHeapUsageDominatedBySearch (#6463) (#6465)

(cherry picked from commit 55cc109)

Signed-off-by: PritLadani <pritkladani@gmail.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

server/src/test/java/org/opensearch/search/backpressure/trackers/HeapUsageTrackerTests.java

@@ -12,13 +12,16 @@
 import org.opensearch.action.search.SearchTask;
 import org.opensearch.common.settings.ClusterSettings;
 import org.opensearch.common.settings.Settings;
+import org.opensearch.monitor.jvm.JvmStats;
 import org.opensearch.search.backpressure.settings.SearchBackpressureSettings;
 import org.opensearch.search.backpressure.settings.SearchShardTaskSettings;
 import org.opensearch.search.backpressure.settings.SearchTaskSettings;
+import org.opensearch.tasks.CancellableTask;
 import org.opensearch.tasks.Task;
 import org.opensearch.tasks.TaskCancellation;
 import org.opensearch.test.OpenSearchTestCase;
 
+import java.util.List;
 import java.util.Optional;
 
 import static org.mockito.Mockito.spy;
@@ -140,4 +143,17 @@ public void testNotEligibleForCancellation() {
         reason = tracker.checkAndMaybeGetCancellationReason(task);
         assertFalse(reason.isPresent());
     }
+
+    public void testIsHeapUsageDominatedBySearch() {
+        assumeTrue("Skip the test if the hardware doesn't support heap usage tracking", HeapUsageTracker.isHeapTrackingSupported());
+
+        // task with 1 byte of heap usage so that it does not breach the threshold
+        CancellableTask task = createMockTaskWithResourceStats(SearchShardTask.class, 1, 1);
+        assertFalse(HeapUsageTracker.isHeapUsageDominatedBySearch(List.of(task), 0.5));
+
+        long totalHeap = JvmStats.jvmStats().getMem().getHeapMax().getBytes();
+        // task with heap usage of [totalHeap - 1] so that it breaches the threshold
+        task = createMockTaskWithResourceStats(SearchShardTask.class, 1, totalHeap - 1);
+        assertTrue(HeapUsageTracker.isHeapUsageDominatedBySearch(List.of(task), 0.5));
+    }
 }