GH-3557: Adjust the replication factor for transactions topic on @emb…

…eddedkafka

Fixes: #3557 

#3557

 * Adjust the replication factor for the transaction state topic on `EmbeddedKafka` based on the broker count in 
  `EmbeddedKafka`.
* Keep the default replication factor of 3. 
* Adding tests to verify

spring-kafka-test/src/main/java/org/springframework/kafka/test/context/EmbeddedKafkaContextCustomizer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2023 the original author or authors.
+ * Copyright 2017-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -47,13 +47,16 @@
  * @author Oleg Artyomov
  * @author Sergio Lourenco
  * @author Pawel Lozinski
+ * @author Seonghwan Lee
  *
  * @since 1.3
  */
 class EmbeddedKafkaContextCustomizer implements ContextCustomizer {
 
 	private final EmbeddedKafka embeddedKafka;
 
+	private final String TRANSACTION_STATE_LOG_REPLICATION_FACTOR = "transaction.state.log.replication.factor";
+
 	EmbeddedKafkaContextCustomizer(EmbeddedKafka embeddedKafka) {
 		this.embeddedKafka = embeddedKafka;
 	}
@@ -121,6 +124,8 @@ public void customizeContext(ConfigurableApplicationContext context, MergedConte
 			}
 		}
 
+		properties.putIfAbsent(TRANSACTION_STATE_LOG_REPLICATION_FACTOR, String.valueOf(Math.min(3, embeddedKafka.count())));
+
 		embeddedKafkaBroker.brokerProperties((Map<String, String>) (Map<?, ?>) properties);
 		if (StringUtils.hasText(this.embeddedKafka.bootstrapServersProperty())) {
 			embeddedKafkaBroker.brokerListProperty(this.embeddedKafka.bootstrapServersProperty());

spring-kafka-test/src/test/java/org/springframework/kafka/test/context/EmbeddedKafkaContextCustomizerTests.java

@@ -16,6 +16,8 @@
 
 package org.springframework.kafka.test.context;
 
+import java.util.Map;
+
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -25,13 +27,15 @@
 import org.springframework.kafka.test.EmbeddedKafkaBroker;
 import org.springframework.kafka.test.utils.KafkaTestUtils;
 
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
  * @author Oleg Artyomov
  * @author Sergio Lourenco
  * @author Artem Bilan
  * @author Gary Russell
+ * @author Seonghwan Lee
  *
  * @since 1.3
  */
@@ -91,6 +95,21 @@ void testMulti() {
 				.matches("127.0.0.1:[0-9]+,127.0.0.1:[0-9]+");
 	}
 
+	@Test
+	void testTransactionReplicationFactor() {
+		EmbeddedKafka annotationWithPorts =
+				AnnotationUtils.findAnnotation(TestWithEmbeddedKafkaTransactionFactor.class, EmbeddedKafka.class);
+		EmbeddedKafkaContextCustomizer customizer = new EmbeddedKafkaContextCustomizer(annotationWithPorts);
+		ConfigurableApplicationContext context = new GenericApplicationContext();
+		customizer.customizeContext(context, null);
+		context.refresh();
+
+		EmbeddedKafkaBroker embeddedKafkaBroker = context.getBean(EmbeddedKafkaBroker.class);
+		Map<String, Object> properties = (Map<String, Object>) KafkaTestUtils.getPropertyValue(embeddedKafkaBroker, "brokerProperties");
+
+		assertThat(properties.get("transaction.state.log.replication.factor")).isEqualTo("2");
+	}
+
 	@EmbeddedKafka(kraft = false)
 	private static final class TestWithEmbeddedKafka {
 
@@ -111,4 +130,9 @@ private static final class TestWithEmbeddedKafkaMulti {
 
 	}
 
+	@EmbeddedKafka(kraft = false, count = 2)
+	private static final class TestWithEmbeddedKafkaTransactionFactor {
+
+	}
+
 }