private void produceData(final List<String> inputValues) {
        final Properties producerProp = new Properties();
        producerProp.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, CLUSTER.bootstrapServers());
        producerProp.put(ProducerConfig.ACKS_CONFIG, "all");
        producerProp.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
        producerProp.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);

        IntegrationTestUtils.produceValuesSynchronously(DEFAULT_INPUT_TOPIC, inputValues, producerProp, mockTime);
    }
Tests related to internal topics in streams
streams/src/test/java/org/apache/kafka/streams/integration/InternalTopicIntegrationTest.java