public List<V> readValuesToList() {
        final List<V> output = new LinkedList<>();
        V outputValue;
        while (!isEmpty()) {
            outputValue = readValue();
            output.add(outputValue);
        }
        return output;
    }
Read all values from topic to List.

@return List of output values.
streams/test-utils/src/main/java/org/apache/kafka/streams/TestOutputTopic.java