Use List.copyOf() and add test

Author: ivancea

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/Driver.java

@@ -556,7 +556,7 @@ private void updateStatus(long extraCpuNanos, int extraIterations, DriverStatus.
                 prev.cpuNanos() + extraCpuNanos,
                 prev.iterations() + extraIterations,
                 status,
-                new ArrayList<>(statusOfCompletedOperators),
+                List.copyOf(statusOfCompletedOperators),
                 activeOperators.stream().map(op -> new OperatorStatus(op.toString(), op.status())).toList(),
                 sleeps
             );

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/operator/DriverTests.java

@@ -47,8 +47,13 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.LongSupplier;
 
+import static net.bytebuddy.matcher.ElementMatchers.is;
+import static org.hamcrest.Matchers.any;
+import static org.hamcrest.Matchers.comparesEqualTo;
 import static org.hamcrest.Matchers.either;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.not;
+import static org.hamcrest.Matchers.sameInstance;
 
 public class DriverTests extends ESTestCase {
     /**
@@ -204,6 +209,39 @@ public void testProfileAndStatusInterval() {
         assertThat(driver.profile().iterations(), equalTo((long) inPages.size()));
     }
 
+    public void testUnchangedStatus() {
+        DriverContext driverContext = driverContext();
+        List<Page> inPages = randomList(2, 100, DriverTests::randomPage);
+        List<Page> outPages = new ArrayList<>();
+
+        long startEpoch = randomNonNegativeLong();
+        long startNanos = randomLong();
+        long waitTime = randomLongBetween(10000, 100000);
+        long tickTime = randomLongBetween(10000, 100000);
+        long statusInterval = randomLongBetween(1, 10);
+
+        Driver driver = createDriver(startEpoch, startNanos, driverContext, inPages, outPages, TimeValue.timeValueNanos(statusInterval));
+
+        NowSupplier nowSupplier = new NowSupplier(startNanos, waitTime, tickTime);
+
+        int iterationsPerTick = randomIntBetween(1, 10);
+
+        for (int i = 0; i < inPages.size(); i += iterationsPerTick) {
+            DriverStatus initialStatus = driver.status();
+            long completedOperatorsHash = initialStatus.completedOperators().hashCode();
+            long activeOperatorsHash = initialStatus.activeOperators().hashCode();
+            long sleepsHash = initialStatus.sleeps().hashCode();
+
+            driver.run(TimeValue.timeValueDays(10), iterationsPerTick, nowSupplier);
+
+            DriverStatus newStatus = driver.status();
+            assertThat(newStatus, not(sameInstance(initialStatus)));
+            assertThat(newStatus.completedOperators() != initialStatus.completedOperators() || newStatus.completedOperators().hashCode() == completedOperatorsHash, equalTo(true));
+            assertThat(newStatus.activeOperators() != initialStatus.activeOperators() || newStatus.activeOperators().hashCode() == activeOperatorsHash, equalTo(true));
+            assertThat(newStatus.sleeps() != initialStatus.sleeps() || newStatus.sleeps().hashCode() == sleepsHash, equalTo(true));
+        }
+    }
+
     private static Driver createDriver(
         long startEpoch,
         long startNanos,