Enforce JDK version on CI server

Add a test to ensure that the CI server does not accidentally build
with the wrong JDK version.

Issue: SPR-10569

spring-core/src/test/java/org/springframework/tests/BuildTests.java

+/*
+ * Copyright 2002-2013 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
+ *
+ * http://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.tests;
+
+import org.junit.Test;
+
+import static org.hamcrest.Matchers.*;
+import static org.junit.Assert.*;
+
+/**
+ * General build related tests. Part of spring-core to ensure that they run early in the
+ * build process.
+ */
+public class BuildTests {
+
+	@Test
+	public void javaVersion() throws Exception {
+		Assume.group(TestGroup.CI);
+		assertThat("Java Version", JavaVersion.runningVersion(), equalTo(JavaVersion.JAVA_18));
+	}
+
+}

spring-core/src/test/java/org/springframework/tests/TestGroup.java

@@ -54,7 +54,12 @@ public enum TestGroup {
 	 * Tests requiring the presence of jmxremote_optional.jar in jre/lib/ext in order to
 	 * avoid "Unsupported protocol: jmxmp" errors.
 	 */
-	JMXMP;
+	JMXMP,
+
+	/**
+	 * Tests that should only be run on the continuous integration server.
+	 */
+	CI;
 
 
 	/**

spring-core/src/test/java/org/springframework/tests/TestGroupTests.java

@@ -64,7 +64,7 @@ public class TestGroupTests {
 		thrown.expect(IllegalArgumentException.class);
 		thrown.expectMessage("Unable to find test group 'missing' when parsing " +
 				"testGroups value: 'performance, missing'. Available groups include: " +
-				"[LONG_RUNNING,PERFORMANCE,JMXMP]");
+				"[LONG_RUNNING,PERFORMANCE,JMXMP,CI]");
 		TestGroup.parse("performance, missing");
 	}