simplify test to not use lambda at all

core/src/test/java/org/elasticsearch/index/IndexServiceTests.java

@@ -27,7 +27,6 @@ import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
-import org.elasticsearch.common.util.concurrent.CountDown;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
@@ -43,7 +42,6 @@ import java.io.IOException;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
-import java.util.function.BiFunction;
 
 import static org.elasticsearch.index.query.QueryBuilders.termQuery;
 import static org.hamcrest.Matchers.containsString;
@@ -190,18 +188,12 @@ public class IndexServiceTests extends ESSingleNodeTestCase {
             }
         };
 
-        BiFunction<AtomicReference<CountDownLatch>, CountDownLatch, CountDownLatch> swapAndReturn = (ref, newLatch) -> {
-            CountDownLatch downLatch = ref.get();
-            ref.set(newLatch);
-            return downLatch;
-        };
         latch.get().await();
-        swapAndReturn.apply(latch, new CountDownLatch(1));
+        latch.set(new CountDownLatch(1));
         assertEquals(1, count.get());
         // here we need to swap first before we let it go otherwise threads might be very fast and run that task twice due to
         // random exception and the schedule interval is 1ms
-        swapAndReturn.apply(latch2, new CountDownLatch(1)).countDown();
-
+        latch2.getAndSet(new CountDownLatch(1)).countDown();
         latch.get().await();
         assertEquals(2, count.get());
         task.close();