Run multiple selected test methods in a single JVM (#1836)

[wenytang-ms]

When several test methods of the same class are selected in the Test Explorer, vscode-java-test currently launches one JVM per method, which makes Spring-style tests (where each JVM rebuilds the ApplicationContext in @BeforeAll) extremely slow.

Group methods of the same class into one launch and rely on the new 'Class:method' line format supported by the bundled Eclipse JDT JUnit runtime so that all selected methods are discovered inside a single JVM, sharing per-class @BeforeAll/@afterall lifecycle and any cached fixture (e.g. Spring ApplicationContext).

Methods restricted to a single invocation (uniqueId) keep their own launch, since the underlying protocol carries at most one uniqueId per JVM.

[wenytang-ms]

depends on eclipse-jdt/eclipse.jdt.ui#2975

[Copilot]

Pull request overview

This PR improves performance when running multiple selected test methods from the same class by batching them into a single JVM launch (to reuse per-class lifecycle and cached fixtures like Spring’s ApplicationContext). It also adds a compatibility fallback: when the bundled Eclipse JDT JUnit runtime is too old to support the new multi-method Class:method line format, the extension silently retries by launching each method in its own JVM.

Changes:

• Batch method-level selections by parent class (while keeping uniqueId-restricted invocations isolated) and export mergeTestMethods for unit testing.
• Add a TypeScript-side marker-based detection to silently fall back to per-method launches on legacy JDT-LS.
• Add Java-side detection of JUnit runtime capability/version and emit a marked error to trigger the fallback; write multi-method Class:method entries to -testNameFile.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/suite/testController.mergeTestMethods.test.ts	Adds unit tests covering method batching, class upgrade, and uniqueId isolation.
src/controller/testController.ts	Implements method batching logic, adds silent fallback retry flow, and introduces isolated per-item launch helper.
src/constants.ts	Introduces the shared marker prefix constant used to detect legacy multi-method support.
java-extension/.../JUnitLaunchUtils.java	Adds runtime bundle version detection and the marker constant on the Java side.
java-extension/.../JUnitLaunchConfigurationDelegate.java	Uses -testNameFile for multi-method launches and throws a marked error when unsupported.

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