public KeyValue<K, V> readKeyValue() {
        final TestRecord<K, V> record = readRecord();
        return new KeyValue<>(record.key(), record.value());
    }
Read one record from the output topic and return its key and value as pair.

@return Next output as {@link KeyValue}.
streams/test-utils/src/main/java/org/apache/kafka/streams/TestOutputTopic.java