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 {

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

@@ -19,11 +19,21 @@
 class ClasspathFilters {
 
 	static final String CLASS_FILE_SUFFIX = ".class";
+	static final String SOURCE_FILE_SUFFIX = ".java";
+
+	// System property defined since Java 12: https://bugs.java/bugdatabase/JDK-8210877
+	private static final boolean SOURCE_MODE = System.getProperty("jdk.launcher.sourcefile") != null;
+
 	private static final String PACKAGE_INFO_FILE_NAME = "package-info" + CLASS_FILE_SUFFIX;
 	private static final String MODULE_INFO_FILE_NAME = "module-info" + CLASS_FILE_SUFFIX;
 
+	static boolean isClassOrSourceFileName(String name) {
+		return name.endsWith(CLASS_FILE_SUFFIX) || (SOURCE_MODE && name.endsWith(SOURCE_FILE_SUFFIX));
+	}
+
 	static Predicate<Path> classFiles() {
-		return file -> isNotPackageInfo(file) && isNotModuleInfo(file) && isClassFile(file);
+		return file -> isNotPackageInfo(file) && isNotModuleInfo(file)
+				&& (isClassFile(file) || (SOURCE_MODE && isSourceFile(file)));
 	}
 
 	static Predicate<Path> resourceFiles() {
@@ -42,6 +52,10 @@ private static boolean isClassFile(Path file) {
 		return file.getFileName().toString().endsWith(CLASS_FILE_SUFFIX);
 	}
 
+	private static boolean isSourceFile(Path file) {
+		return file.getFileName().toString().endsWith(SOURCE_FILE_SUFFIX);
+	}
+
 	private ClasspathFilters() {
 	}
 

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

@@ -11,7 +11,6 @@
 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.StringUtils.isNotBlank;
 
 import java.io.IOException;
@@ -32,6 +31,7 @@
 import java.util.function.Supplier;
 import java.util.stream.Stream;
 
+import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.function.Try;
 import org.junit.platform.commons.io.Resource;
@@ -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));
@@ -253,21 +253,29 @@ 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 determineSimpleClassName(Path file) {
+		String fileName = file.getFileName().toString();
+		return determineSimpleClassName(fileName);
+	}
+
+	static String determineSimpleClassName(String fileName) {
+		int lastDot = fileName.lastIndexOf('.');
+		if (lastDot < 0) {
+			throw new JUnitException("Expected file name with file extension, but got: " + fileName);
+		}
+		return fileName.substring(0, lastDot);
 	}
 
 	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
+			// TODO: Remove workaround for JDK bug: https://bugs.openjdk.org/browse/JDK-8153248
 			subpackageName = subpackageName.substring(0, subpackageName.length() - pathSeparator.length());
 		}
 		return subpackageName;

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

@@ -253,9 +253,11 @@ 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)
+					return names.filter(ClasspathFilters::isClassOrSourceFileName)
+							.map(DefaultClasspathScanner::determineSimpleClassName)
+							.map(name -> name.replace('/', '.'))
 							.filter(name -> !"module-info".equals(name))
+							.filter(name -> !name.endsWith("package-info"))
 							.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.
 		 *

junit-platform-console/junit-platform-console.gradle.kts

@@ -27,6 +27,7 @@ dependencies {
 tasks {
 	compileJava {
 		options.compilerArgs.addAll(listOf(
+			"-Xlint:-module", // due to qualified exports
 			"--add-modules", "info.picocli",
 			"--add-reads", "${javaModuleName}=info.picocli"
 		))

junit-platform-console/src/main/java/module-info.java

@@ -24,5 +24,7 @@
 	requires org.junit.platform.launcher;
 	requires org.junit.platform.reporting;
 
+	exports org.junit.platform.console.output to org.junit.start;
+
 	provides java.util.spi.ToolProvider with org.junit.platform.console.ConsoleLauncherToolProvider;
 }

junit-start/junit-start.gradle.kts

@@ -0,0 +1,21 @@
+plugins {
+	id("junitbuild.java-library-conventions")
+}
+
+description = "JUnit Start Module"
+
+dependencies {
+	api(platform(projects.junitBom))
+	api(projects.junitJupiter)
+
+	compileOnlyApi(libs.apiguardian)
+	compileOnlyApi(libs.jspecify)
+	compileOnlyApi(projects.junitJupiterEngine)
+
+	implementation(projects.junitPlatformLauncher)
+	implementation(projects.junitPlatformConsole)
+}
+
+backwardCompatibilityChecks {
+	enabled = false // already checked by individual projects
+}

junit-start/src/main/java/module-info.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2015-2025 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
+ */
+
+/**
+ * Defines the API of the JUnit Start module for writing and running tests.
+ * <p>
+ * Usage example:
+ * <pre>{@code
+ * import module org.junit.start;
+ *
+ *  void main() {
+ *    JUnit.run();
+ *  }
+ *
+ *  @Test
+ *  void addition() {
+ *    Assertions.assertEquals(2, 1 + 1, "Addition error detected!");
+ *  }
+ * }</pre>
+ */
+module org.junit.start {
+	requires static transitive org.apiguardian.api;
+	requires static transitive org.jspecify;
+
+	requires transitive org.junit.jupiter;
+	requires org.junit.platform.launcher;
+	requires org.junit.platform.console;
+
+	exports org.junit.start;
+}

junit-start/src/main/java/org/junit/start/JUnit.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2015-2025 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.start;
+
+import static java.lang.StackWalker.Option.RETAIN_CLASS_REFERENCE;
+import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
+import static org.junit.platform.engine.discovery.DiscoverySelectors.selectModule;
+import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
+
+import java.io.PrintWriter;
+import java.nio.charset.Charset;
+
+import org.apiguardian.api.API;
+import org.junit.platform.commons.JUnitException;
+import org.junit.platform.console.output.ColorPalette;
+import org.junit.platform.console.output.Theme;
+import org.junit.platform.console.output.TreePrintingListener;
+import org.junit.platform.engine.DiscoverySelector;
+import org.junit.platform.launcher.core.LauncherFactory;
+import org.junit.platform.launcher.listeners.SummaryGeneratingListener;
+
+@API(status = EXPERIMENTAL, since = "6.0")
+public final class JUnit {
+	/**
+	 * Run all tests defined in the caller class.
+	 */
+	public static void run() {
+		var walker = StackWalker.getInstance(RETAIN_CLASS_REFERENCE);
+		run(selectClass(walker.getCallerClass()));
+	}
+
+	/**
+	 * Run all tests defined in the given test class.
+	 * @param testClass  the class to discover and execute tests in
+	 */
+	public static void run(Class<?> testClass) {
+		run(selectClass(testClass));
+	}
+
+	/**
+	 * Run all tests defined in the given module.
+	 * @param testModule the module to discover and execute tests in
+	 */
+	public static void run(Module testModule) {
+		run(selectModule(testModule));
+	}
+
+	private static void run(DiscoverySelector selector) {
+		var listener = new SummaryGeneratingListener();
+		var charset = Charset.defaultCharset();
+		var writer = new PrintWriter(System.out, true, charset);
+		var printer = new TreePrintingListener(writer, ColorPalette.DEFAULT, Theme.valueOf(charset));
+		var request = request().selectors(selector).forExecution() //
+				.listeners(listener, printer) //
+				.build();
+		var launcher = LauncherFactory.create();
+		launcher.execute(request);
+		var summary = listener.getSummary();
+
+		if (summary.getTotalFailureCount() == 0)
+			return;
+
+		summary.printFailuresTo(new PrintWriter(System.err, true, charset));
+		throw new JUnitException("JUnit run finished with %d failure%s".formatted( //
+			summary.getTotalFailureCount(), //
+			summary.getTotalFailureCount() == 1 ? "" : "s"));
+	}
+
+	private JUnit() {
+	}
+}

junit-start/src/main/java/org/junit/start/package-info.java

@@ -0,0 +1,8 @@
+/**
+ * Contains JUnit Start API for writing and running tests.
+ */
+
+@NullMarked
+package org.junit.start;
+
+import org.jspecify.annotations.NullMarked;

platform-tooling-support-tests/platform-tooling-support-tests.gradle.kts

@@ -20,6 +20,7 @@ javaLibrary {
 spotless {
 	java {
 		target(files(project.java.sourceSets.map { it.allJava }), "projects/**/*.java")
+		targetExclude("projects/junit-start/**/*.java") // due to compact source files and module imports
 	}
 	kotlin {
 		target("projects/**/*.kt")

platform-tooling-support-tests/projects/jar-describe-module/junit-platform-console.expected.txt

@@ -7,9 +7,9 @@ requires org.junit.platform.engine
 requires org.junit.platform.launcher
 requires org.junit.platform.reporting
 provides java.util.spi.ToolProvider with org.junit.platform.console.ConsoleLauncherToolProvider
+qualified exports org.junit.platform.console.output to org.junit.start
 contains org.junit.platform.console
 contains org.junit.platform.console.command
 contains org.junit.platform.console.options
-contains org.junit.platform.console.output
 contains org.junit.platform.console.shadow.picocli
 main-class org.junit.platform.console.ConsoleLauncher

platform-tooling-support-tests/projects/jar-describe-module/junit-start.expected.txt

@@ -0,0 +1,8 @@
+org.junit.start@${version} jar:file:.+/junit-start-\d.+\.jar..module-info\.class
+exports org.junit.start
+requires java.base mandated
+requires org.apiguardian.api static transitive
+requires org.jspecify static transitive
+requires org.junit.jupiter transitive
+requires org.junit.platform.console
+requires org.junit.platform.launcher