private void newFetchConfigFromValues() {
        new FetchConfig(ConsumerConfig.DEFAULT_FETCH_MIN_BYTES,
                ConsumerConfig.DEFAULT_FETCH_MAX_BYTES,
                ConsumerConfig.DEFAULT_FETCH_MAX_WAIT_MS,
                ConsumerConfig.DEFAULT_MAX_PARTITION_FETCH_BYTES,
                ConsumerConfig.DEFAULT_MAX_POLL_RECORDS,
                true,
                ConsumerConfig.DEFAULT_CLIENT_RACK,
                IsolationLevel.READ_UNCOMMITTED);
    }
Verify correctness if both the key and value {@link Deserializer deserializers} provided to the
{@link FetchConfig} constructors are {@code nonnull}.
clients/src/test/java/org/apache/kafka/clients/consumer/internals/FetchConfigTest.java