fix: reuse Jupiter finder for JUnit 6 discovery

[wenyt (wenytang-ms)]

Summary

• reuse the inherited Jupiter finder for JUnit 6 test discovery
• remove the divergent JUnit6TestFinder implementation
• add regression coverage for package-private, non-static @Nested JUnit 6 classes

Root cause

The custom JUnit 6 finder passed the JUnit 6 kind to CoreTestSearchEngine.isAccessibleClass(). Eclipse JDT currently applies Jupiter's relaxed @Nested accessibility rules only through JUnit5TestFinder, so valid nested classes could be rejected during container discovery and lazy loading.

JUnit 5 and JUnit 6 share the same Jupiter discovery semantics. The JUnit 6 searcher now inherits JUnit5TestFinder while retaining TestKind.JUnit6 and the JUnit 6 JDT kind for runtime selection.

Upstream alignment

JDT LS runs the JUnit support provided by Eclipse JDT's org.eclipse.jdt.junit.core bundle. Eclipse JDT's merged JUnit 6 implementation explicitly shares the JUnit 5 finder while selecting a separate JUnit 6 runtime:

• The JUnit 6 test kind maps finderClass to JUnit5TestFinder, while loaderPluginId and loaderClass point to the JUnit 6 runtime: plugin.xml lines 112-117.
• The upstream JUnit 6 finder test states, "We re-use JUnit5TestFinder for JUnit 6": JUnit6TestFinderJupiterTest.java lines 49-54.
• The same test asserts that resolving the JUnit 6 container kind returns an instance of JUnit5TestFinder: JUnit6TestFinderJupiterTest.java lines 116-122.
• Eclipse JDT tracks renaming the class to JUnitJupiterTestFinder specifically because it is reused for JUnit 6: eclipse-jdt.ui#2620.

This PR follows that upstream separation: shared Jupiter discovery through JUnit5TestFinder, with the JUnit 6 kind retained for launch/runtime selection.

Validation

.\java-extension\mvnw.cmd -f java-extension\pom.xml clean verify -Dtest=JUnit6TestSearcherTest -Dsurefire.failIfNoSpecifiedTests=false -Declipse.p2.mirrors=false
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

Addresses the test discovery and missing CodeLens portion of #1897. The individual-method launch hang still requires separate verification.

[Copilot]

Pull request overview

This PR fixes JUnit 6 test discovery by reusing Eclipse JDT’s existing Jupiter (JUnit 5) test finder logic, eliminating a divergent JUnit 6 finder that applied stricter accessibility rules and incorrectly rejected valid @Nested classes.

Changes:

• Make JUnit6TestSearcher inherit JUnit 5’s finder-based discovery behavior while still reporting TestKind.JUnit6 / JUnit 6 JDT kind IDs for runtime selection.
• Remove the custom JUnit6TestFinder implementation.
• Add regression coverage and a minimal workspace project for package-private, non-static @Nested JUnit 6 classes.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
java-extension/com.microsoft.java.test.plugin/src/main/java/com/microsoft/java/test/plugin/searcher/JUnit6TestSearcher.java	Drops custom finder usage and relies on inherited Jupiter discovery, keeping JUnit 6 kind identifiers.
java-extension/com.microsoft.java.test.plugin/src/main/java/com/microsoft/java/test/plugin/searcher/JUnit6TestFinder.java	Removes the divergent JUnit 6 finder implementation that caused incorrect accessibility filtering.
java-extension/com.microsoft.java.test.plugin/META-INF/MANIFEST.MF	Exports the searcher package to the test bundle via x-friends so the new test can access searchers.
java-extension/com.microsoft.java.test.plugin.test/src/com/microsoft/java/test/plugin/searcher/JUnit6TestSearcherTest.java	Adds a regression test validating discovery of a non-static, package-private @Nested class under JUnit 6.
java-extension/com.microsoft.java.test.plugin.test/projects/junit6-nested/src/test/java/example/NestedTests.java	Adds a sample JUnit 6 nested test case used by the regression test.
java-extension/com.microsoft.java.test.plugin.test/projects/junit6-nested/.project	Adds Eclipse project metadata for the regression test workspace project.
java-extension/com.microsoft.java.test.plugin.test/projects/junit6-nested/.classpath	Adds JDT classpath configuration using JUNIT_CONTAINER/6 for the regression test workspace project.

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.