Fix package name comparison on Java 8 (#4077)

`Class.getPackage()` returns `null` for the default package on Java 8.
This is now handled by inspecting the fully qualified class name rather
than throwing a `NullPointerException`.

Fixes #4076.

documentation/src/docs/asciidoc/release-notes/release-notes-5.11.3.adoc

@@ -16,7 +16,8 @@ on GitHub.
 [[release-notes-5.11.3-junit-platform-bug-fixes]]
 ==== Bug Fixes
 
-* ❓
+* Fixed a regression in method search algorithms introduced in 5.11.0 when classes reside
+  in the default package and using a Java 8 runtime.
 
 [[release-notes-5.11.3-junit-platform-deprecations-and-breaking-changes]]
 ==== Deprecations and Breaking Changes

junit-platform-commons/junit-platform-commons.gradle.kts

@@ -29,6 +29,7 @@ tasks.jar {
 
 tasks.codeCoverageClassesJar {
 	exclude("org/junit/platform/commons/util/ModuleUtils.class")
+	exclude("org/junit/platform/commons/util/PackageNameUtils.class")
 }
 
 eclipse {

junit-platform-commons/src/main/java/org/junit/platform/commons/util/PackageNameUtils.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2015-2024 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.commons.util;
+
+import static org.junit.platform.commons.util.PackageUtils.DEFAULT_PACKAGE_NAME;
+
+/**
+ * Collection of utilities for working with package names.
+ *
+ * <h2>DISCLAIMER</h2>
+ *
+ * <p>These utilities are intended solely for usage within the JUnit framework
+ * itself. <strong>Any usage by external parties is not supported.</strong>
+ * Use at your own risk!
+ *
+ * @since 1.11.3
+ */
+class PackageNameUtils {
+
+	static String getPackageName(Class<?> clazz) {
+		Package p = clazz.getPackage();
+		if (p != null) {
+			return p.getName();
+		}
+		String className = clazz.getName();
+		int index = className.lastIndexOf('.');
+		return index == -1 ? DEFAULT_PACKAGE_NAME : className.substring(0, index);
+	}
+
+}

junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java

@@ -19,6 +19,7 @@
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.apiguardian.api.API.Status.STABLE;
 import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
+import static org.junit.platform.commons.util.PackageNameUtils.getPackageName;
 import static org.junit.platform.commons.util.ReflectionUtils.HierarchyTraversalMode.BOTTOM_UP;
 import static org.junit.platform.commons.util.ReflectionUtils.HierarchyTraversalMode.TOP_DOWN;
 
@@ -1903,7 +1904,7 @@ private static boolean isPackagePrivate(Member member) {
 	}
 
 	private static boolean declaredInSamePackage(Method m1, Method m2) {
-		return m1.getDeclaringClass().getPackage().getName().equals(m2.getDeclaringClass().getPackage().getName());
+		return getPackageName(m1.getDeclaringClass()).equals(getPackageName(m2.getDeclaringClass()));
 	}
 
 	/**

junit-platform-commons/src/main/java9/org/junit/platform/commons/util/PackageNameUtils.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2015-2024 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.commons.util;
+
+/**
+ * Collection of utilities for working with package names.
+ *
+ * <h2>DISCLAIMER</h2>
+ *
+ * <p>These utilities are intended solely for usage within the JUnit framework
+ * itself. <strong>Any usage by external parties is not supported.</strong>
+ * Use at your own risk!
+ *
+ * @since 1.11.3
+ */
+class PackageNameUtils {
+
+	static String getPackageName(Class<?> clazz) {
+		return clazz.getPackageName();
+	}
+
+}

platform-tooling-support-tests/projects/vintage/src/test/java/DefaultPackageTest.java

@@ -0,0 +1,22 @@
+
+/*
+ * Copyright 2015-2024 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+import com.example.vintage.VintageTest;
+
+import org.junit.Ignore;
+
+/**
+ * Reproducer for https://github.com/junit-team/junit5/issues/4076
+ */
+@Ignore
+public class DefaultPackageTest extends VintageTest {
+	void packagePrivateMethod() {
+	}
+}

platform-tooling-support-tests/projects/vintage/src/test/java/com/example/vintage/VintageTest.java

@@ -15,6 +15,9 @@
 import org.junit.Test;
 
 public class VintageTest {
+	void packagePrivateMethod() {
+	}
+
 	@Test
 	public void success() {
 		// pass