Introduce org.junit.start module

build.gradle.kts

@@ -43,7 +43,7 @@ val vintageProjects by extra(listOf(
 	dependencyProject(projects.junitVintageEngine)
 ))
 
-val mavenizedProjects by extra(platformProjects + jupiterProjects + vintageProjects)
+val mavenizedProjects by extra(listOf(dependencyProject(projects.junitStart)) + platformProjects + jupiterProjects + vintageProjects)
 val modularProjects by extra(mavenizedProjects - setOf(dependencyProject(projects.junitPlatformConsoleStandalone)))
 
 dependencies {

documentation/src/docs/asciidoc/link-attributes.adoc

@@ -230,6 +230,8 @@ endif::[]
 // Jupiter Migration Support
 :EnableJUnit4MigrationSupport:               {javadoc-root}/org.junit.jupiter.migrationsupport/org/junit/jupiter/migrationsupport/EnableJUnit4MigrationSupport.html[@EnableJUnit4MigrationSupport]
 :EnableRuleMigrationSupport:                 {javadoc-root}/org.junit.jupiter.migrationsupport/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupport.html[@EnableRuleMigrationSupport]
+// JUnit Start
+:JUnit:                                      {javadoc-root}/org.junit.start/org/junit/start/JUnit.html[JUnit]
 // Vintage
 :junit-vintage-engine:                       {javadoc-root}/org.junit.vintage.engine/org/junit/vintage/engine/package-summary.html[junit-vintage-engine]
 // Examples Repository
@@ -247,6 +249,8 @@ endif::[]
 :Checkstyle:                                 https://checkstyle.sourceforge.io[Checkstyle]
 :DiscussionsQA:                              https://github.com/junit-team/junit-framework/discussions/categories/q-a[Q&A category on GitHub Discussions]
 :Hamcrest:                                   https://hamcrest.org/JavaHamcrest/[Hamcrest]
+:JEP511:                                     https://openjdk.org/jeps/511[JEP 511]
+:JEP512:                                     https://openjdk.org/jeps/512[JEP 512]
 :Jimfs:                                      https://google.github.io/jimfs/[Jimfs]
 :Log4j:                                      https://logging.apache.org/log4j/2.x/[Log4j]
 :Log4j_JDK_Logging_Adapter:                  https://logging.apache.org/log4j/2.x/log4j-jul/index.html[Log4j JDK Logging Adapter]

documentation/src/docs/asciidoc/release-notes/release-notes-6.1.0-M1.adoc

@@ -52,6 +52,17 @@ repository on GitHub.
 [[release-notes-6.1.0-M1-junit-jupiter-new-features-and-improvements]]
 ==== New Features and Improvements
 
+* Introduce new module `org.junit.start` for writing and running tests. It simplifies
+  usages of JUnit in compact source files together with a single module import statement:
+[source,java,indent=0]
+----
+import module org.junit.start;
+
+void main() { JUnit.run(); }
+
+@Test
+void test() { Assertions.assertEquals(2, 1 + 1); }
+----
 * Introduce new `dynamicTest(Consumer<? super Configuration>)` factory method for dynamic
   tests. It allows configuring the `ExecutionMode` of the dynamic test in addition to its
   display name, test source URI, and executable.

documentation/src/docs/asciidoc/user-guide/running-tests.adoc

@@ -836,6 +836,40 @@ DYNAMIC = 35
 REPORTED = 37
 ----
 
+[[running-tests-source-launcher]]
+=== Source Launcher
+
+Java 25 introduced Module Import Declarations with {JEP511} and Compact Source Files
+and Instance Methods with {JEP512}. The `org.junit.start` module is JUnit's "On-Ramp"
+enabler, allowing to write minimal source code programs. For example, like in a
+`HelloTests.java` file reading:
+
+```java
+import module org.junit.start;
+
+void main() {
+  JUnit.run();
+}
+
+@Test
+void stringLength() {
+  Assertions.assertEquals(11, "Hello JUnit".length());
+}
+```
+With all required modular JAR files available in a local `lib/` directory, the
+following Java 25+ command will discover and execute tests using the JUnit Platform.
+It will also print the result tree to the console.
+
+```shell
+java --module-path lib --add-modules org.junit.start HelloTests.java
+╷
+└─ JUnit Jupiter ✔
+   └─ HelloTests ✔
+      └─ stringLength() ✔
+```
+
+Find JUnit's class API documentation here: {JUnit}
+
 [[running-tests-discovery-selectors]]
 === Discovery Selectors
 

documentation/src/javadoc/junit-overview.html

@@ -1,6 +1,6 @@
 <body>
 
-<p>This document consists of three sections:</p>
+<p>This document consists of four sections:</p>
 
 <dl>
     <dt>Platform</dt>
@@ -12,13 +12,16 @@
     </dd>
     <dt>Jupiter</dt>
     <dd>JUnit Jupiter is the combination of the programming model and extension model for
-        writing JUnit tests and extensions. The Jupiter sub-project provides a TestEngine
+        writing JUnit tests and extensions. The Jupiter subproject provides a TestEngine
         for running Jupiter based tests on the platform.
     </dd>
     <dt>Vintage</dt>
     <dd>JUnit Vintage provides a TestEngine for running JUnit 3 and JUnit 4 based tests on the
         platform.
     </dd>
+    <dt>Other Modules</dt>
+    <dd>This section lists all modules that are not part of a dedicated section.
+    </dd>
 </dl>
 
 <p>Already consulted the <a href="../user-guide/index.html">JUnit User Guide</a>?</p>

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

@@ -11,7 +11,9 @@
 package org.junit.platform.commons.util;
 
 import static java.util.stream.Collectors.joining;
-import static org.junit.platform.commons.util.ClasspathFilters.CLASS_FILE_SUFFIX;
+import static org.junit.platform.commons.util.SearchPathUtils.PACKAGE_SEPARATOR_CHAR;
+import static org.junit.platform.commons.util.SearchPathUtils.PACKAGE_SEPARATOR_STRING;
+import static org.junit.platform.commons.util.SearchPathUtils.determineSimpleClassName;
 import static org.junit.platform.commons.util.StringUtils.isNotBlank;
 
 import java.io.IOException;
@@ -57,8 +59,6 @@ class DefaultClasspathScanner implements ClasspathScanner {
 	private static final char CLASSPATH_RESOURCE_PATH_SEPARATOR = '/';
 	private static final String CLASSPATH_RESOURCE_PATH_SEPARATOR_STRING = String.valueOf(
 		CLASSPATH_RESOURCE_PATH_SEPARATOR);
-	private static final char PACKAGE_SEPARATOR_CHAR = '.';
-	private static final String PACKAGE_SEPARATOR_STRING = String.valueOf(PACKAGE_SEPARATOR_CHAR);
 
 	/**
 	 * Malformed class name InternalError like reported in #401.
@@ -132,7 +132,7 @@ private List<Class<?>> findClassesForUris(List<URI> baseUris, String basePackage
 	private List<Class<?>> findClassesForUri(URI baseUri, String basePackageName, ClassFilter classFilter) {
 		List<Class<?>> classes = new ArrayList<>();
 		// @formatter:off
-		walkFilesForUri(baseUri, ClasspathFilters.classFiles(),
+		walkFilesForUri(baseUri, SearchPathUtils::isClassOrSourceFile,
 				(baseDir, file) ->
 						processClassFileSafely(baseDir, basePackageName, classFilter, file, classes::add));
 		// @formatter:on
@@ -156,7 +156,7 @@ private List<Resource> findResourcesForUris(List<URI> baseUris, String basePacka
 	private List<Resource> findResourcesForUri(URI baseUri, String basePackageName, ResourceFilter resourceFilter) {
 		List<Resource> resources = new ArrayList<>();
 		// @formatter:off
-		walkFilesForUri(baseUri, ClasspathFilters.resourceFiles(),
+		walkFilesForUri(baseUri, SearchPathUtils::isResourceFile,
 				(baseDir, file) ->
 						processResourceFileSafely(baseDir, basePackageName, resourceFilter, file, resources::add));
 		// @formatter:on
@@ -182,10 +182,10 @@ private static void walkFilesForUri(URI baseUri, Predicate<Path> filter, BiConsu
 		}
 	}
 
-	private void processClassFileSafely(Path baseDir, String basePackageName, ClassFilter classFilter, Path classFile,
+	private void processClassFileSafely(Path baseDir, String basePackageName, ClassFilter classFilter, Path file,
 			Consumer<Class<?>> classConsumer) {
 		try {
-			String fullyQualifiedClassName = determineFullyQualifiedClassName(baseDir, basePackageName, classFile);
+			String fullyQualifiedClassName = determineFullyQualifiedClassName(baseDir, basePackageName, file);
 			if (classFilter.match(fullyQualifiedClassName)) {
 				try {
 					// @formatter:off
@@ -196,12 +196,12 @@ private void processClassFileSafely(Path baseDir, String basePackageName, ClassF
 					// @formatter:on
 				}
 				catch (InternalError internalError) {
-					handleInternalError(classFile, fullyQualifiedClassName, internalError);
+					handleInternalError(file, fullyQualifiedClassName, internalError);
 				}
 			}
 		}
 		catch (Throwable throwable) {
-			handleThrowable(classFile, throwable);
+			handleThrowable(file, throwable);
 		}
 	}
 
@@ -221,12 +221,12 @@ private void processResourceFileSafely(Path baseDir, String basePackageName, Res
 		}
 	}
 
-	private String determineFullyQualifiedClassName(Path baseDir, String basePackageName, Path classFile) {
+	private String determineFullyQualifiedClassName(Path baseDir, String basePackageName, Path file) {
 		// @formatter:off
 		return Stream.of(
 					basePackageName,
-					determineSubpackageName(baseDir, classFile),
-					determineSimpleClassName(classFile)
+					determineSubpackageName(baseDir, file),
+					determineSimpleClassName(file)
 				)
 				.filter(value -> !value.isEmpty()) // Handle default package appropriately.
 				.collect(joining(PACKAGE_SEPARATOR_STRING));
@@ -253,24 +253,14 @@ private String determineFullyQualifiedResourceName(Path baseDir, String basePack
 		// @formatter:on
 	}
 
-	private String determineSimpleClassName(Path classFile) {
-		String fileName = classFile.getFileName().toString();
-		return fileName.substring(0, fileName.length() - CLASS_FILE_SUFFIX.length());
-	}
-
 	private String determineSimpleResourceName(Path resourceFile) {
 		return resourceFile.getFileName().toString();
 	}
 
-	private String determineSubpackageName(Path baseDir, Path classFile) {
-		Path relativePath = baseDir.relativize(classFile.getParent());
+	private String determineSubpackageName(Path baseDir, Path file) {
+		Path relativePath = baseDir.relativize(file.getParent());
 		String pathSeparator = baseDir.getFileSystem().getSeparator();
-		String subpackageName = relativePath.toString().replace(pathSeparator, PACKAGE_SEPARATOR_STRING);
-		if (subpackageName.endsWith(pathSeparator)) {
-			// Workaround for JDK bug: https://bugs.openjdk.java.net/browse/JDK-8153248
-			subpackageName = subpackageName.substring(0, subpackageName.length() - pathSeparator.length());
-		}
-		return subpackageName;
+		return relativePath.toString().replace(pathSeparator, PACKAGE_SEPARATOR_STRING);
 	}
 
 	private void handleInternalError(Path classFile, String fullyQualifiedClassName, InternalError ex) {

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

@@ -41,6 +41,8 @@
 @API(status = INTERNAL, since = "1.0")
 public final class ExceptionUtils {
 
+	private static final String JUNIT_START_PACKAGE_PREFIX = "org.junit.start.";
+
 	private static final String JUNIT_PLATFORM_LAUNCHER_PACKAGE_PREFIX = "org.junit.platform.launcher.";
 
 	private static final Predicate<String> STACK_TRACE_ELEMENT_FILTER = ClassNamePatternFilterUtils //
@@ -139,6 +141,9 @@ public static void pruneStackTrace(Throwable throwable, List<String> classNames)
 				prunedStackTrace.addAll(stackTrace.subList(i, stackTrace.size()));
 				break;
 			}
+			else if (className.startsWith(JUNIT_START_PACKAGE_PREFIX)) {
+				prunedStackTrace.clear();
+			}
 			else if (className.startsWith(JUNIT_PLATFORM_LAUNCHER_PACKAGE_PREFIX)) {
 				prunedStackTrace.clear();
 			}

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

@@ -24,6 +24,7 @@
 import java.lang.module.ResolvedModule;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -253,9 +254,10 @@ List<Class<?>> scan(ModuleReference reference) {
 			try (ModuleReader reader = reference.open()) {
 				try (Stream<String> names = reader.list()) {
 					// @formatter:off
-					return names.filter(name -> name.endsWith(".class"))
-							.map(this::className)
-							.filter(name -> !"module-info".equals(name))
+					return names.filter(name -> !name.endsWith("/")) // remove directories
+							.map(Path::of)
+							.filter(SearchPathUtils::isClassOrSourceFile)
+							.map(SearchPathUtils::determineFullyQualifiedClassName)
 							.filter(classFilter::match)
 							.<Class<?>> map(this::loadClassUnchecked)
 							.filter(classFilter::match)
@@ -268,15 +270,6 @@ List<Class<?>> scan(ModuleReference reference) {
 			}
 		}
 
-		/**
-		 * Convert resource name to binary class name.
-		 */
-		private String className(String resourceName) {
-			resourceName = resourceName.substring(0, resourceName.length() - 6); // 6 = ".class".length()
-			resourceName = resourceName.replace('/', '.');
-			return resourceName;
-		}
-
 		/**
 		 * Load class by its binary name.
 		 *