Cleanup HotThreadsIT (example of test cleanup) (#115601)

Just a quick example of how to save quite a few lines of code and make
a test easier to reason about.

Author: original-brownbear

server/src/internalClusterTest/java/org/elasticsearch/action/admin/HotThreadsIT.java

@@ -10,7 +10,7 @@
 
 import org.apache.logging.log4j.Level;
 import org.apache.lucene.util.Constants;
-import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.ActionFuture;
 import org.elasticsearch.action.admin.cluster.node.hotthreads.NodeHotThreads;
 import org.elasticsearch.action.admin.cluster.node.hotthreads.NodesHotThreadsRequest;
 import org.elasticsearch.action.admin.cluster.node.hotthreads.NodesHotThreadsResponse;
@@ -26,15 +26,14 @@
 import org.hamcrest.Matcher;
 
 import java.util.Map;
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.ExecutionException;
 
 import static org.elasticsearch.index.query.QueryBuilders.boolQuery;
 import static org.elasticsearch.index.query.QueryBuilders.matchAllQuery;
 import static org.elasticsearch.index.query.QueryBuilders.termQuery;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertHitCount;
+import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertResponse;
 import static org.hamcrest.CoreMatchers.equalTo;
-import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.notNullValue;
 import static org.hamcrest.Matchers.allOf;
 import static org.hamcrest.Matchers.containsString;
@@ -44,11 +43,10 @@
 
 public class HotThreadsIT extends ESIntegTestCase {
 
-    public void testHotThreadsDontFail() throws InterruptedException {
+    public void testHotThreadsDontFail() throws InterruptedException, ExecutionException {
         // This test just checks if nothing crashes or gets stuck etc.
         createIndex("test");
         final int iters = scaledRandomIntBetween(2, 20);
-        final AtomicBoolean hasErrors = new AtomicBoolean(false);
         for (int i = 0; i < iters; i++) {
             final NodesHotThreadsRequest request = new NodesHotThreadsRequest(
                 Strings.EMPTY_ARRAY,
@@ -67,36 +65,7 @@ public void testHotThreadsDontFail() throws InterruptedException {
                     randomBoolean()
                 )
             );
-            final CountDownLatch latch = new CountDownLatch(1);
-            client().execute(TransportNodesHotThreadsAction.TYPE, request, new ActionListener<>() {
-                @Override
-                public void onResponse(NodesHotThreadsResponse nodeHotThreads) {
-                    boolean success = false;
-                    try {
-                        assertThat(nodeHotThreads, notNullValue());
-                        Map<String, NodeHotThreads> nodesMap = nodeHotThreads.getNodesMap();
-                        assertThat(nodeHotThreads.failures(), empty());
-                        assertThat(nodesMap.size(), equalTo(cluster().size()));
-                        for (NodeHotThreads ht : nodeHotThreads.getNodes()) {
-                            assertNotNull(ht.getHotThreads());
-                        }
-                        success = true;
-                    } finally {
-                        if (success == false) {
-                            hasErrors.set(true);
-                        }
-                        latch.countDown();
-                    }
-                }
-
-                @Override
-                public void onFailure(Exception e) {
-                    logger.error("FAILED", e);
-                    hasErrors.set(true);
-                    latch.countDown();
-                    fail();
-                }
-            });
+            final ActionFuture<NodesHotThreadsResponse> hotThreadsFuture = client().execute(TransportNodesHotThreadsAction.TYPE, request);
 
             indexRandom(
                 true,
@@ -105,7 +74,7 @@ public void onFailure(Exception e) {
                 prepareIndex("test").setId("3").setSource("field1", "value3")
             );
             ensureSearchable();
-            while (latch.getCount() > 0) {
+            while (hotThreadsFuture.isDone() == false) {
                 assertHitCount(
                     prepareSearch().setQuery(matchAllQuery())
                         .setPostFilter(
@@ -115,8 +84,15 @@ public void onFailure(Exception e) {
                     3L
                 );
             }
-            safeAwait(latch);
-            assertThat(hasErrors.get(), is(false));
+            assertResponse(hotThreadsFuture, nodeHotThreads -> {
+                assertThat(nodeHotThreads, notNullValue());
+                Map<String, NodeHotThreads> nodesMap = nodeHotThreads.getNodesMap();
+                assertThat(nodeHotThreads.failures(), empty());
+                assertThat(nodesMap.size(), equalTo(cluster().size()));
+                for (NodeHotThreads ht : nodeHotThreads.getNodes()) {
+                    assertNotNull(ht.getHotThreads());
+                }
+            });
         }
     }