@Test
    public void testStartWithEarlyStartListeners() {
        StandardAuthorizer authorizer = new StandardAuthorizer();
        authorizer.configure(Collections.singletonMap(SUPER_USERS_CONFIG, "User:superman"));
        Map<Endpoint, ? extends CompletionStage<Void>> futures2 = authorizer.
            start(new AuthorizerTestServerInfo(Arrays.asList(PLAINTEXT, CONTROLLER)));
        assertEquals(new HashSet<>(Arrays.asList(PLAINTEXT, CONTROLLER)), futures2.keySet());
        assertFalse(futures2.get(PLAINTEXT).toCompletableFuture().isDone());
        assertTrue(futures2.get(CONTROLLER).toCompletableFuture().isDone());
    }
Test that StandardAuthorizer#start returns a completed future for early start
listeners.
metadata/src/test/java/org/apache/kafka/metadata/authorizer/StandardAuthorizerTest.java