public final Set<String> producedTopicNames() {
        return Collections.unmodifiableSet(outputRecordsByTopic.keySet());
    }
Get all the names of all the topics to which records have been produced during the test run.
<p>
Call this method after piping the input into the test driver to retrieve the full set of topic names the topology
produced records to.
<p>
The returned set of topic names may include user (e.g., output) and internal (e.g., changelog, repartition) topic
names.

@return the set of topic names the topology has produced to
streams/test-utils/src/main/java/org/apache/kafka/streams/TopologyTestDriver.java