Transform Health API YAML test to Java REST test

This test failed occasionally due to the health node not having
received the health info from all nodes yet, resulting in an
"unknown" status. In a Java test, we do have the option to retry.

qa/smoke-test-http/src/javaRestTest/java/org/elasticsearch/http/HealthReportIT.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.http;
+
+import org.elasticsearch.client.Request;
+import org.elasticsearch.client.Response;
+import org.elasticsearch.test.XContentTestUtils;
+import org.elasticsearch.test.rest.ESRestTestCase;
+
+public class HealthReportIT extends ESRestTestCase {
+
+    /**
+     * This test is a Java REST test instead of a YAML one, as the health node might need some time before it has received the health info
+     * from all the nodes. Until it has received all health info, the status will be "unknown", so we'll wait until the status turns green.
+     */
+    public void testGetHealth() throws Exception {
+        Request request = new Request("GET", "_health_report");
+        Response response = client().performRequest(request);
+        assertBusy(() -> {
+            assertEquals(200, response.getStatusLine().getStatusCode());
+            var mapView = XContentTestUtils.createJsonMapView(response.getEntity().getContent());
+            assertEquals("green", mapView.get("status"));
+            assertEquals("green", mapView.get("indicators.master_is_stable.status"));
+            assertEquals("The cluster has a stable master node", mapView.get("indicators.master_is_stable.symptom"));
+        });
+    }
+}