apply @rjernst review comments

core/src/main/java/org/elasticsearch/indices/IndicesService.java

@@ -271,7 +271,6 @@ public class IndicesService extends AbstractLifecycleComponent<IndicesService> i
                 idxSettings.getNumberOfReplicas(),
                 idxSettings.isShadowReplicaIndex() ? "s" : "");
 
-        // plugin modules must be added here, before others or we can get crazy injection errors...
         final IndexModule indexModule = new IndexModule(idxSettings, indexStoreConfig, analysisRegistry);
         pluginsService.onIndexModule(indexModule);
         for (IndexEventListener listener : builtInListeners) {

core/src/main/java/org/elasticsearch/indices/memory/IndexingMemoryController.java

@@ -423,7 +423,7 @@ public class IndexingMemoryController extends AbstractLifecycleComponent<Indexin
 
     @Override
     public void onShardActive(IndexShard indexShard) {
-        // At least on shard used to be inactive ie. a new write operation just showed up.
+        // At least one shard used to be inactive ie. a new write operation just showed up.
         // We try to fix the shards indexing buffer immediately. We could do this async instead, but cost should
         // be low, and it's rare this happens.
         forceCheck();

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

@@ -29,7 +29,6 @@ import org.elasticsearch.Version;
 import org.elasticsearch.cache.recycler.PageCacheRecycler;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
-import org.elasticsearch.common.inject.ModuleTestCase;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.BigArrays;
@@ -60,6 +59,7 @@ import org.elasticsearch.script.ScriptContextRegistry;
 import org.elasticsearch.script.ScriptEngineService;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.script.mustache.MustacheScriptEngineService;
+import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.IndexSettingsModule;
 import org.elasticsearch.test.engine.MockEngineFactory;
 import org.elasticsearch.threadpool.ThreadPool;
@@ -74,7 +74,7 @@ import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Consumer;
 
-public class IndexModuleTests extends ModuleTestCase {
+public class IndexModuleTests extends ESTestCase {
     private Index index;
     private Settings settings;
     private IndexSettings indexSettings;

core/src/test/java/org/elasticsearch/index/cache/bitset/BitSetFilterCacheTests.java

@@ -188,6 +188,7 @@ public class BitSetFilterCacheTests extends ESTestCase {
             new BitsetFilterCache(INDEX_SETTINGS, warmer, null);
             fail("listener can't be null");
         } catch (IllegalArgumentException ex) {
+            assertEquals("listener must not be null", ex.getMessage());
             // all is well
         }
     }