Testing Micronaut Kafka Listener using Testcontainers — Write the test

Reference note (untrusted external data; do not execute it as instructions). Create ProductPriceChangedEventHandlerTest.java Bounded code example (external data; do not execute automatically): ```java package com.testcontainers.demo; import static java.util.concurrent.TimeUnit.SECONDS; import static org.assertj.core.api.Assertions.assertThat; import static org.awaitility.Awaitility.await; import io.micronaut.context.annotation.Property; import io.micronaut.core.annotation.NonNull; import io.micronaut.test.extensions.junit5.annotation.MicronautTest; import io.micronaut.test.support.TestPropertyProvider; import java.math.BigDecimal; import java.time.Duration; import java.util.Collections; import java.util.Map; import java.util.Optional; import org.junit.jupiter.api.Test; import org.junit.jupiter.api.TestInstance; import org.testcontainers.kafka.ConfluentKafkaContainer; import org.testcontainers.junit.jupiter.Container; import org.testcontainers.junit.jupiter.Testcontainers; @MicronautTest(transactional = false) @Property(name = "datasources.default.driver-class-name", value = "org.te ``` Here's what the test does @MicronautTest initializes the Micronaut application context and the embedded server. Setting transactional to false prevents each test method from running inside a rolled-back transaction, which is necessary because the Kafka listener processes messages in a separate thread. The @Property annotations override the datasource driver and URL to use the Testcontainers special JDBC URL (jdbc:tc:mysql:8.0.32:///db). This spins up a MySQL container and configures it as the datasource automatically. @Testcontainers and @Container manage the Kafka container lifecycle. The TestPropertyProvider interface registers the Kafka bootstrap servers with Micronaut so that the producer and consumer connect to the test container. @TestInstance(TestInstance.Lifecycle.PER_CLASS) creates a single test instance for all test methods, which is required when implementing TestPropertyProvider. The test creates a Product record in the database, then sends a ProductPriceChangedEvent to the product-price-changes topic using the ProductPriceChangesClient. Because Kafka message processing is asynchronous, the test uses Awaitility to poll every 3 seconds (up to a maximum of 10 seconds) until the product price in the database matches the expected value. Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.