Add integration tests for validateMultiReleaseJar task

This commit also renames the "validateJar" task to
"validateMultiReleaseJar".

Closes gh-35768

buildSrc/src/main/java/org/springframework/build/multirelease/MultiReleaseJarPlugin.java

@@ -41,6 +41,8 @@ import org.gradle.jvm.toolchain.JavaToolchainService;
  */
 public class MultiReleaseJarPlugin implements Plugin<Project> {
 
+	public static String VALIDATE_JAR_TASK_NAME = "validateMultiReleaseJar";
+
 	@Inject
 	protected JavaToolchainService getToolchains() {
 		throw new UnsupportedOperationException();
@@ -60,7 +62,7 @@ public class MultiReleaseJarPlugin implements Plugin<Project> {
 				tasks,
 				dependencies,
 				objects);
-		TaskProvider<MultiReleaseJarValidateTask> validateJarTask = tasks.register("validateJar", MultiReleaseJarValidateTask.class, (task) -> {
+		TaskProvider<MultiReleaseJarValidateTask> validateJarTask = tasks.register(VALIDATE_JAR_TASK_NAME, MultiReleaseJarValidateTask.class, (task) -> {
 			task.getJar().set(tasks.named("jar", Jar.class).flatMap(AbstractArchiveTask::getArchiveFile));
 		});
 		tasks.named("check", task -> task.dependsOn(validateJarTask));

buildSrc/src/main/java/org/springframework/build/multirelease/MultiReleaseJarValidateTask.java

@@ -27,11 +27,14 @@ import java.util.List;
 
 @CacheableTask
 public abstract class MultiReleaseJarValidateTask extends JavaExec {
+
 	@InputFile
 	@PathSensitive(PathSensitivity.RELATIVE)
 	public abstract RegularFileProperty getJar();
+
 	public MultiReleaseJarValidateTask() {
 		getMainModule().set("jdk.jartool");
 		getArgumentProviders().add(() -> List.of("--validate", "--file", getJar().get().getAsFile().getAbsolutePath()));
 	}
+
 }

buildSrc/src/test/java/org/springframework/build/multirelease/MultiReleaseJarPluginTests.java

@@ -26,11 +26,13 @@ import java.util.jar.Attributes;
 import java.util.jar.JarFile;
 import org.gradle.testkit.runner.BuildResult;
 import org.gradle.testkit.runner.GradleRunner;
+import org.gradle.testkit.runner.UnexpectedBuildFailure;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 /**
  * Tests for {@link MultiReleaseJarPlugin}
@@ -116,6 +118,31 @@ public class MultiReleaseJarPluginTests {
 		}
 	}
 
+	@Test
+	void validateJar() throws IOException {
+		writeBuildFile("""
+				plugins {
+					id 'java'
+					id 'org.springframework.build.multiReleaseJar'
+				}
+				version = '1.2.3'
+				multiRelease { releaseVersions 17 }
+				""");
+		writeClass("src/main/java17", "Main.java", """
+				public class Main {
+				
+					public void method() {}
+				
+				}
+				""");
+		writeClass("src/main/java", "Main.java", """
+				public class Main {}
+				""");
+		assertThatThrownBy(() ->runGradle("validateMultiReleaseJar"))
+				.isInstanceOf(UnexpectedBuildFailure.class)
+				.hasMessageContaining("entry: META-INF/versions/17/Main.class, has a class version incompatible with an earlier version");
+	}
+
 	private void writeBuildFile(String buildContent) throws IOException {
 		try (PrintWriter out = new PrintWriter(new FileWriter(this.buildFile))) {
 			out.print(buildContent);