Adapt testFollowStatsApiIncludeShardFollowStatsWithRemovedFollowerIndex (elastic#44801)

This commit unmutes and renames the test that failed on CI (elastic#44796)
after elastic#44702 has been merged.

This test assumes that follow stats still exist after a follower index has
been deleted. The follow stats are based on persistent tasks, and
since elastic#44702 the persistent tasks of deleted following indices are now
 automatically cleaned up to avoid to bloat the cluster state.

I don't think we should report any follow stats for deleted indices and I
don't think that this test makes much sense now the tasks are cleaned
up. This is why the test has been renamed.

closes elastic#44796

Author: tlrx

x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/FollowStatsIT.java

@@ -30,6 +30,7 @@
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.elasticsearch.xpack.ccr.LocalIndexFollowingIT.getIndexSettings;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasSize;
 import static org.hamcrest.collection.IsEmptyCollection.empty;
 
 /*
@@ -149,9 +150,8 @@ public void testFollowStatsApiResourceNotFound() throws Exception {
         assertAcked(client().execute(PauseFollowAction.INSTANCE, new PauseFollowAction.Request("follower1")).actionGet());
     }
 
-    public void testFollowStatsApiIncludeShardFollowStatsWithRemovedFollowerIndex() throws Exception {
-        final String leaderIndexSettings = getIndexSettings(1, 0,
-            singletonMap(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(), "true"));
+    public void testFollowStatsApiWithDeletedFollowerIndex() throws Exception {
+        final String leaderIndexSettings = getIndexSettings(1, 0, singletonMap(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(), "true"));
         assertAcked(client().admin().indices().prepareCreate("leader1").setSource(leaderIndexSettings, XContentType.JSON));
         ensureGreen("leader1");
 
@@ -171,18 +171,11 @@ public void testFollowStatsApiIncludeShardFollowStatsWithRemovedFollowerIndex()
 
         assertAcked(client().admin().indices().delete(new DeleteIndexRequest("follower1")).actionGet());
 
-        statsRequest = new FollowStatsAction.StatsRequest();
-        response = client().execute(FollowStatsAction.INSTANCE, statsRequest).actionGet();
-        assertThat(response.getStatsResponses().size(), equalTo(1));
-        assertThat(response.getStatsResponses().get(0).status().followerIndex(), equalTo("follower1"));
-
-        statsRequest = new FollowStatsAction.StatsRequest();
-        statsRequest.setIndices(new String[] {"follower1"});
-        response = client().execute(FollowStatsAction.INSTANCE, statsRequest).actionGet();
-        assertThat(response.getStatsResponses().size(), equalTo(1));
-        assertThat(response.getStatsResponses().get(0).status().followerIndex(), equalTo("follower1"));
-
-        assertAcked(client().execute(PauseFollowAction.INSTANCE, new PauseFollowAction.Request("follower1")).actionGet());
+        assertBusy(() -> {
+            FollowStatsAction.StatsRequest request = new FollowStatsAction.StatsRequest();
+            FollowStatsAction.StatsResponses statsResponse = client().execute(FollowStatsAction.INSTANCE, request).actionGet();
+            assertThat(statsResponse.getStatsResponses(), hasSize(0));
+        });
     }
 
     public void testFollowStatsApiIncludeShardFollowStatsWithClosedFollowerIndex() throws Exception {