private <K, V> Map<TopicPartition, List<ConsumerRecord<K, V>>> fetchRecords() {
        Fetch<K, V> fetch = collectFetch();
        return fetch.records();
    }
Assert that the {@link Fetcher#collectFetch() latest fetch} does not contain any
{@link Fetch#records() user-visible records}, did not
{@link Fetch#positionAdvanced() advance the consumer's position},
and is {@link Fetch#isEmpty() empty}.
@param reason the reason to include for assertion methods such as {@link org.junit.jupiter.api.Assertions#assertTrue(boolean, String)}
clients/src/test/java/org/apache/kafka/clients/consumer/internals/FetcherTest.java