public List<TestRecord<K, V>> readRecordsToList() {
        final List<TestRecord<K, V>> output = new LinkedList<>();
        while (!isEmpty()) {
            output.add(readRecord());
        }
        return output;
    }
Read output to List.
This method can be used if the result is considered a stream.
If the result is considered a table, the list will contain all updated, ie, a key might be contained multiple times.
If you are only interested in the last table update (ie, the final table state),
you can use {@link #readKeyValuesToMap()} instead.

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