@Test
    public void shouldGetToRunningWithWindowedTableInFKJ() throws Exception {
        final String appID = APP_ID + "-windowed-FKJ";
        streamsProp.put(StreamsConfig.APPLICATION_ID_CONFIG, appID);

        final StreamsBuilder streamsBuilder = new StreamsBuilder();
        final KStream<String, String> inputTopic = streamsBuilder.stream(DEFAULT_INPUT_TOPIC);
        final KTable<String, String> inputTable = streamsBuilder.table(DEFAULT_INPUT_TABLE_TOPIC);
        inputTopic
            .groupBy(
                (k, v) -> k,
                Grouped.with("GroupName", Serdes.String(), Serdes.String())
            )
            .windowedBy(TimeWindows.of(Duration.ofMinutes(10)))
            .aggregate(
                () -> "",
                (k, v, a) -> a + k)
            .leftJoin(
                inputTable,
                v -> v,
                (x, y) -> x + y
            );

        try (final KafkaStreams streams = new KafkaStreams(streamsBuilder.build(), streamsProp)) {
            startApplicationAndWaitUntilRunning(streams);
        }
    }
Tests related to internal topics in streams
streams/src/test/java/org/apache/kafka/streams/integration/InternalTopicIntegrationTest.java