fix: reuse Jupiter finder for JUnit 6 discovery

java-extension/com.microsoft.java.test.plugin.test/projects/junit6-nested/.classpath

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+    <classpathentry kind="src" output="target/test-classes" path="src/test/java">
+        <attributes>
+            <attribute name="test" value="true"/>
+        </attributes>
+    </classpathentry>
+    <classpathentry kind="con"
+        path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-17"/>
+    <classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/6"/>
+    <classpathentry kind="output" path="target/test-classes"/>
+</classpath>

java-extension/com.microsoft.java.test.plugin.test/projects/junit6-nested/.project

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+    <name>junit6-nested</name>
+    <comment></comment>
+    <projects>
+    </projects>
+    <buildSpec>
+        <buildCommand>
+            <name>org.eclipse.jdt.core.javabuilder</name>
+            <arguments>
+            </arguments>
+        </buildCommand>
+    </buildSpec>
+    <natures>
+        <nature>org.eclipse.jdt.core.javanature</nature>
+    </natures>
+</projectDescription>

java-extension/com.microsoft.java.test.plugin.test/projects/junit6-nested/src/test/java/example/NestedTests.java

@@ -0,0 +1,15 @@
+package example;
+
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+class NestedTests {
+
+    @Nested
+    class MemberTests {
+
+        @Test
+        void testNested() {
+        }
+    }
+}

java-extension/com.microsoft.java.test.plugin.test/src/com/microsoft/java/test/plugin/searcher/JUnit6TestSearcherTest.java

@@ -0,0 +1,53 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Microsoft Corporation and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Microsoft Corporation - initial API and implementation
+ *******************************************************************************/
+
+package com.microsoft.java.test.plugin.searcher;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+import java.util.List;
+import java.util.Set;
+
+import org.eclipse.core.resources.IProject;
+import org.eclipse.core.runtime.NullProgressMonitor;
+import org.eclipse.jdt.core.IJavaProject;
+import org.eclipse.jdt.core.IType;
+import org.eclipse.jdt.core.JavaCore;
+import org.eclipse.jdt.internal.junit.launcher.TestKindRegistry;
+import org.junit.Test;
+
+import com.microsoft.java.test.plugin.AbstractProjectsManagerBasedTest;
+import com.microsoft.java.test.plugin.model.TestKind;
+
+public class JUnit6TestSearcherTest extends AbstractProjectsManagerBasedTest {
+
+    @Test
+    public void testFindNonStaticNestedTestClass() throws Exception {
+        final List<IProject> projects = importProjects("junit6-nested");
+        final IJavaProject javaProject = JavaCore.create(projects.get(0));
+        final IType outerType = javaProject.findType("example.NestedTests");
+        assertNotNull(outerType);
+
+        final IType nestedType = outerType.getType("MemberTests");
+        assertTrue(nestedType.exists());
+
+        final JUnit6TestSearcher searcher = new JUnit6TestSearcher();
+        assertTrue(searcher.isTestClass(nestedType));
+
+        final Set<IType> discoveredTypes = searcher.findTestItemsInContainer(
+                nestedType, new NullProgressMonitor());
+        assertTrue(discoveredTypes.contains(nestedType));
+        assertEquals(TestKind.JUnit6, searcher.getTestKind());
+        assertEquals(TestKindRegistry.JUNIT6_TEST_KIND_ID, searcher.getJdtTestKind());
+    }
+}

java-extension/com.microsoft.java.test.plugin/META-INF/MANIFEST.MF

@@ -53,6 +53,7 @@ Require-Bundle: org.eclipse.jdt.core,
  org.jacoco.core;bundle-version="[0.8.15,0.8.16)"
 Export-Package: com.microsoft.java.test.plugin.launchers;x-friends:="com.microsoft.java.test.plugin.test",
  com.microsoft.java.test.plugin.model;x-friends:="com.microsoft.java.test.plugin.test",
+ com.microsoft.java.test.plugin.searcher;x-friends:="com.microsoft.java.test.plugin.test",
  com.microsoft.java.test.plugin.coverage;x-friends:="com.microsoft.java.test.plugin.test",
  com.microsoft.java.test.plugin.coverage.model;x-friends:="com.microsoft.java.test.plugin.test"
 Bundle-ClassPath: .