Support explicit ClassLoader in NestedClassSelector

Issue: #3298

Author: marcphilipp

documentation/src/docs/asciidoc/release-notes/release-notes-5.10.0-M1.adoc

@@ -37,9 +37,9 @@ repository on GitHub.
   `ClassLoader`. This allows parameter types to be resolved with custom `ClassLoader`
   arrangements (such as OSGi). Consequently, `DiscoverySelectors.selectMethod(Class<?>,
   String, String)` also now works properly with custom `ClassLoader` arrangements.
-* New overloaded constructors for `ClassSelector` and `MethodSelector` that take an
-  explicit `ClassLoader` as a parameter, allowing selectors to select classes in custom
-  `ClassLoader` arrangements like in OSGi.
+* New overloaded constructors for `ClassSelector`, `NestedClassSelector`, and
+  `MethodSelector` that take an explicit `ClassLoader` as a parameter, allowing selectors
+  to select classes in custom `ClassLoader` arrangements like in OSGi.
 * For consistency with JUnit Jupiter lifecycle callbacks, listener method pairs for
   started/finished and opened/closed events are now invoked using "wrapping" semantics.
   This means that finished/closed event methods are invoked in reverse order compared to

junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectors.java

@@ -635,9 +635,26 @@ public static NestedClassSelector selectNestedClass(List<Class<?>> enclosingClas
 	 */
 	@API(status = STABLE, since = "1.6")
 	public static NestedClassSelector selectNestedClass(List<String> enclosingClassNames, String nestedClassName) {
+		return selectNestedClass(enclosingClassNames, nestedClassName, null);
+	}
+
+	/**
+	 * Create a {@code NestedClassSelector} for the supplied class name, its enclosing
+	 * classes' names, and class loader.
+	 *
+	 * @param enclosingClassNames the names of the enclosing classes; never {@code null} or empty
+	 * @param nestedClassName the name of the nested class to select; never {@code null} or blank
+	 * @param classLoader the class loader to use to load the enclosing and nested classes, or
+	 * {@code null} to signal that the default {@code ClassLoader} should be used
+	 * @since 1.10
+	 * @see NestedClassSelector
+	 */
+	@API(status = EXPERIMENTAL, since = "1.10")
+	public static NestedClassSelector selectNestedClass(List<String> enclosingClassNames, String nestedClassName,
+			ClassLoader classLoader) {
 		Preconditions.notEmpty(enclosingClassNames, "Enclosing class names must not be null or empty");
 		Preconditions.notBlank(nestedClassName, "Nested class name must not be null or blank");
-		return new NestedClassSelector(enclosingClassNames, nestedClassName);
+		return new NestedClassSelector(enclosingClassNames, nestedClassName, classLoader);
 	}
 
 	/**

junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedClassSelector.java

@@ -11,7 +11,9 @@
 package org.junit.platform.engine.discovery;
 
 import static java.util.stream.Collectors.toList;
+import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.STABLE;
+import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 
 import java.util.List;
 import java.util.Objects;
@@ -46,17 +48,31 @@
 @API(status = STABLE, since = "1.6")
 public class NestedClassSelector implements DiscoverySelector {
 
-	private List<ClassSelector> enclosingClassSelectors;
-	private ClassSelector nestedClassSelector;
+	private final List<ClassSelector> enclosingClassSelectors;
+	private final ClassSelector nestedClassSelector;
+	private final ClassLoader classLoader;
 
-	NestedClassSelector(List<String> enclosingClassNames, String nestedClassName) {
-		this.enclosingClassSelectors = enclosingClassNames.stream().map(ClassSelector::new).collect(toList());
-		this.nestedClassSelector = new ClassSelector(nestedClassName);
+	NestedClassSelector(List<String> enclosingClassNames, String nestedClassName, ClassLoader classLoader) {
+		this.enclosingClassSelectors = enclosingClassNames.stream() //
+				.map(className -> new ClassSelector(className, classLoader)) //
+				.collect(toUnmodifiableList());
+		this.nestedClassSelector = new ClassSelector(nestedClassName, classLoader);
+		this.classLoader = classLoader;
 	}
 
 	NestedClassSelector(List<Class<?>> enclosingClasses, Class<?> nestedClass) {
 		this.enclosingClassSelectors = enclosingClasses.stream().map(ClassSelector::new).collect(toList());
 		this.nestedClassSelector = new ClassSelector(nestedClass);
+		this.classLoader = nestedClass.getClassLoader();
+	}
+
+	/**
+	 * Get the {@link ClassLoader} used to load the selected nested class.
+	 * @since 1.10
+	 */
+	@API(status = EXPERIMENTAL, since = "1.10")
+	public ClassLoader getClassLoader() {
+		return this.classLoader;
 	}
 
 	/**
@@ -121,6 +137,7 @@ public String toString() {
 		return new ToStringBuilder(this) //
 				.append("enclosingClassNames", getEnclosingClassNames()) //
 				.append("nestedClassName", getNestedClassName()) //
+				.append("classLoader", getClassLoader()) //
 				.toString();
 	}
 

platform-tests/src/test/java/org/junit/platform/engine/discovery/DiscoverySelectorsTests.java

@@ -691,6 +691,27 @@ void selectNestedClassByClassNames() {
 			assertThat(selector.getNestedClassName()).isEqualTo(nestedClassName);
 		}
 
+		@Test
+		void selectNestedClassByClassNamesAndClassLoader() throws Exception {
+			var testClasses = List.of(AbstractClassWithNestedInnerClass.class, ClassWithNestedInnerClass.class,
+				AbstractClassWithNestedInnerClass.NestedClass.class);
+			try (var testClassLoader = TestClassLoader.forClasses(testClasses.toArray(Class[]::new))) {
+
+				var selector = selectNestedClass(List.of(enclosingClassName), nestedClassName, testClassLoader);
+
+				assertThat(selector.getEnclosingClasses()).doesNotContain(ClassWithNestedInnerClass.class);
+				assertThat(selector.getEnclosingClasses()).extracting(Class::getName).containsOnly(enclosingClassName);
+				assertThat(selector.getNestedClass()).isNotEqualTo(AbstractClassWithNestedInnerClass.NestedClass.class);
+				assertThat(selector.getNestedClass().getName()).isEqualTo(nestedClassName);
+
+				assertThat(selector.getClassLoader()).isSameAs(testClassLoader);
+				assertThat(selector.getEnclosingClasses()).extracting(Class::getClassLoader).containsOnly(
+					testClassLoader);
+				assertThat(selector.getNestedClass().getClassLoader()).isSameAs(testClassLoader);
+				assertSame(testClassLoader, selector.getNestedClass().getClassLoader());
+			}
+		}
+
 		@Test
 		void selectDoubleNestedClassByClassNames() {
 			var selector = selectNestedClass(List.of(enclosingClassName, nestedClassName), doubleNestedClassName);

platform-tests/src/test/java/org/junit/platform/engine/discovery/NestedClassSelectorTests.java

@@ -30,18 +30,18 @@ class NestedClassSelectorTests extends AbstractEqualsAndHashCodeTests {
 	@Test
 	void equalsAndHashCode() {
 		var selector1 = new NestedClassSelector(List.of("org.example.EnclosingTestClass"),
-			"org.example.NestedTestClass");
+			"org.example.NestedTestClass", null);
 		var selector2 = new NestedClassSelector(List.of("org.example.EnclosingTestClass"),
-			"org.example.NestedTestClass");
-		var selector3 = new NestedClassSelector(List.of("org.example.X"), "org.example.Y");
+			"org.example.NestedTestClass", null);
+		var selector3 = new NestedClassSelector(List.of("org.example.X"), "org.example.Y", null);
 
 		assertEqualsAndHashCode(selector1, selector2, selector3);
 	}
 
 	@Test
 	void preservesOriginalExceptionWhenTryingToLoadEnclosingClasses() {
-		var selector = new NestedClassSelector(List.of("org.example.EnclosingTestClass"),
-			"org.example.NestedTestClass");
+		var selector = new NestedClassSelector(List.of("org.example.EnclosingTestClass"), "org.example.NestedTestClass",
+			null);
 
 		var exception = assertThrows(PreconditionViolationException.class, selector::getEnclosingClasses);
 
@@ -51,12 +51,23 @@ void preservesOriginalExceptionWhenTryingToLoadEnclosingClasses() {
 
 	@Test
 	void preservesOriginalExceptionWhenTryingToLoadNestedClass() {
-		var selector = new NestedClassSelector(List.of("org.example.EnclosingTestClass"),
-			"org.example.NestedTestClass");
+		var selector = new NestedClassSelector(List.of("org.example.EnclosingTestClass"), "org.example.NestedTestClass",
+			null);
 
 		var exception = assertThrows(PreconditionViolationException.class, selector::getNestedClass);
 
 		assertThat(exception).hasMessage("Could not load class with name: org.example.NestedTestClass") //
 				.hasCauseInstanceOf(ClassNotFoundException.class);
 	}
+
+	@Test
+	void usesClassClassLoader() {
+		var selector = new NestedClassSelector(List.of(getClass()), NestedTestCase.class);
+
+		assertThat(selector.getClassLoader()).isNotNull().isSameAs(getClass().getClassLoader());
+	}
+
+	@SuppressWarnings("InnerClassMayBeStatic")
+	class NestedTestCase {
+	}
 }