Add javadoc

server/src/test/java/org/elasticsearch/action/ActionListenerTests.java

@@ -235,6 +235,11 @@ public void testCompleteWith() {
         assertThat(expectThrows(ExecutionException.class, onFailureListener::get).getCause(), instanceOf(IOException.class));
     }
 
+    /**
+     * Test that map passes the output of the function to its delegate listener and that exceptions in the function are propagated to the
+     * onFailure handler. Also verify that exceptions from ActionListener.onResponse does not invoke onFailure, since it is the
+     * responsibility of the ActionListener implementation (the client of the API) to handle exceptions in onResponse and onFailure.
+     */
     public void testMap() {
         AtomicReference<Exception> exReference = new AtomicReference<>();
 

server/src/test/java/org/elasticsearch/action/admin/indices/create/CreateIndexIT.java

@@ -385,6 +385,10 @@ public void testIndexNameInResponse() {
         assertEquals("Should have index name in response", "foo", response.index());
     }
 
+    /**
+     * Test that when creating a new index successfully, a failure in the ActionListener's onResponse does not result in a call to
+     * onFailure. It is the responsibility of the caller to handle exceptions in the ActionListener's onResponse and onFailure methods.
+     */
     public void testOnResponseFailureOnMaster() throws Exception {
         final String exceptionMessage = randomAlphaOfLength(10);
         final Logger logger = LogManager.getLogger(ClusterApplierService.class);