Add IsolationLevel regression test with Kafka 2.4

This commit makes sure that our copy of the IsolationLevel enum is
consistent with what Kafka 2.4 provides

Closes gh-20822

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/kafka/KafkaPropertiesKafka24Tests.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.kafka;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.autoconfigure.kafka.KafkaProperties.IsolationLevel;
+import org.springframework.boot.testsupport.classpath.ClassPathOverrides;
+import org.springframework.test.util.ReflectionTestUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link KafkaProperties} with Kafka 2.4.
+ *
+ * @author Stephane Nicoll
+ */
+@ClassPathOverrides("org.apache.kafka:kafka-clients:2.4.1")
+class KafkaPropertiesKafka24Tests {
+
+	@Test
+	void isolationLevelEnumConsistentWithKafkaVersion() throws ClassNotFoundException {
+		Class<?> isolationLevelClass = Class.forName("org.apache.kafka.common.requests.IsolationLevel");
+		Object[] original = ReflectionTestUtils.invokeMethod(isolationLevelClass, "values");
+		assertThat(original).extracting("name").containsExactly(IsolationLevel.READ_UNCOMMITTED.name(),
+				IsolationLevel.READ_COMMITTED.name());
+		assertThat(original).extracting("id").containsExactly(IsolationLevel.READ_UNCOMMITTED.id(),
+				IsolationLevel.READ_COMMITTED.id());
+		assertThat(original).hasSize(IsolationLevel.values().length);
+	}
+
+}