Fix SnapshotLifecycleRestIT.testFullPolicySnapshot (#51769)

* Fix SnapshotLifecycleRestIT.testFullPolicySnapshot

This previously was missing some key information in the output of the failure. This captures that
information and adds logging at each step so we can determine the cause *if* it fails again.

Resolves #50358

Author: dakrone

x-pack/plugin/ilm/qa/multi-node/src/test/java/org/elasticsearch/xpack/slm/SnapshotLifecycleRestIT.java

@@ -41,8 +41,10 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
+import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.common.xcontent.XContentFactory.jsonBuilder;
@@ -104,6 +106,11 @@ public void testFullPolicySnapshot() throws Exception {
 
         createSnapshotPolicy(policyName, "snap", "*/1 * * * * ?", repoId, indexName, true);
 
+        // A test for whether the repository's snapshots have any snapshots starting with "snap-"
+        Predicate<Map<String, Object>> repoHasSnapshot = snapMap -> Optional.ofNullable((String) snapMap.get("snapshot"))
+            .map(snapName -> snapName.startsWith("snap-"))
+            .orElse(false);
+
         // Check that the snapshot was actually taken
         assertBusy(() -> {
             Response response = client().performRequest(new Request("GET", "/_snapshot/" + repoId + "/_all"));
@@ -112,17 +119,16 @@ public void testFullPolicySnapshot() throws Exception {
                 snapshotResponseMap = XContentHelper.convertToMap(XContentType.JSON.xContent(), is, true);
             }
             assertThat(snapshotResponseMap.size(), greaterThan(0));
-            final Map<String, Object> snapResponse;
-            try {
-                Map<String, Object> responseMap = ((List<Map<String, Object>>) snapshotResponseMap.get("responses")).get(0);
-                List<Map<String, Object>> snapshots = (List<Map<String, Object>>) responseMap.get("snapshots");
-                assertTrue(snapshots.stream().anyMatch(s -> s.containsKey("snapshot") && s.get("snapshot").toString().startsWith("snap-")));
-                snapResponse = snapshots.get(0);
-            } catch (Exception e) {
-                throw new AssertionError("failed to find snapshot response in " + snapshotResponseMap, e);
-            }
-            assertThat(snapResponse.get("indices"), equalTo(Collections.singletonList(indexName)));
-            Map<String, Object> metadata = (Map<String, Object>) snapResponse.get("metadata");
+            List<Map<String, Object>> snapResponse = ((List<Map<String, Object>>) snapshotResponseMap.get("responses")).stream()
+                .peek(m -> logger.info("--> responses: {}", m))
+                .map(m -> (List<Map<String, Object>>) m.get("snapshots"))
+                .peek(allReposSnapshots -> logger.info("--> all repository's snapshots: {}", allReposSnapshots))
+                .filter(allReposSnapshots -> allReposSnapshots.stream().anyMatch(repoHasSnapshot))
+                .peek(allRepos -> logger.info("--> snapshots with 'snap-' snapshot: {}", allRepos))
+                .findFirst()
+                .orElseThrow(() -> new AssertionError("failed to find snapshot response in " + snapshotResponseMap));
+            assertThat(snapResponse.get(0).get("indices"), equalTo(Collections.singletonList(indexName)));
+            Map<String, Object> metadata = (Map<String, Object>) snapResponse.get(0).get("metadata");
             assertNotNull(metadata);
             assertThat(metadata.get("policy"), equalTo(policyName));
         });