[Maintenance] Track migration from BasePlatformTestCase to native JUnit 5 fixtures

[YangSiJun528]

Summary

Track the upstream support and prerequisites required to migrate the remaining IntelliJ Platform fixture tests from BasePlatformTestCase and JUnit Vintage to native JUnit Jupiter fixtures.

This is a tracking issue rather than an immediate implementation task. It does not block standalone unit tests or visual tests from using Jupiter.

Current state

• The plugin supports IntelliJ Platform builds starting from 241.
• General tests currently target IntelliJ IDEA Community 2024.1.7.
• The current test configuration uses:
  • junit:junit:4.13.2;
  • archunit-junit4;
  • TestFrameworkType.Platform.
• The current baseline is 45 test classes and 286 tests.
• 28 classes and 186 tests depend on BasePlatformTestCase or related JUnit 3-style fixtures.
• The remaining tests consist of 95 JUnit 4 tests and 5 ArchUnit rules.
• IntelliJ Platform 2024.1.7 does not provide the complete composable JUnit 5 fixture API required to replace myFixture, including projectFixture(), moduleFixture(), and codeInsightFixture().

Switching only to useJUnitPlatform() without the Vintage engine would silently stop discovering the existing BasePlatformTestCase tests.

Upstream context

JetBrains/intellij-platform-plugin-template#537 proposed replacing the previous UI Test Robot setup with IntelliJ IDE Starter.

The proposed structure:

• retained JUnit 4 and TestFrameworkType.Platform for the general test source set;
• added a separate uiTest source set and Gradle task;
• configured only uiTest with:
  • TestFrameworkType.Starter;
  • TestFrameworkType.JUnit5;
  • JUnit Jupiter;
  • JUnit Platform Launcher;
  • useJUnitPlatform();
• kept UI tests separate from the normal check workflow.

The PR was closed without being merged and is not present in the current template. It should therefore be treated as a design reference rather than an officially adopted template configuration.

Decision for now

• Keep existing BasePlatformTestCase tests compatible through the Vintage engine if the general test task is moved to JUnit Platform.
• Allow standalone unit tests to migrate to Jupiter independently.
• Add visual tests through a separate JUnit 5 source set and task.
• Keep visual-test implementation separate from this migration.
• Do not raise the minimum supported IntelliJ Platform version solely to remove Vintage.

Revisit when

Re-evaluate the migration when one or more of the following occurs:

• the minimum supported IntelliJ Platform version is raised;
• the published test framework for the minimum version provides stable project, module, editor, and code-insight fixtures;
• the official IntelliJ Platform plugin template adopts native Jupiter fixtures for general tests;
• BasePlatformTestCase or the Vintage engine is deprecated;
• the JUnit 4 runtime workaround for test-framework-junit5 is no longer required.

Migration scope

When the prerequisites are satisfied:

• replace BasePlatformTestCase inheritance with native Jupiter fixtures;
• convert the remaining JUnit 4 annotations and timeout declarations;
• migrate ArchUnit to its JUnit 5 engine;
• remove the Vintage engine;
• remove junit:junit and archunit-junit4;
• preserve the existing test coverage and discovery baseline.

Acceptance criteria

• All tests run through the Jupiter engine.
• No test depends on BasePlatformTestCase or JUnit 3-style testXxx() discovery.
• No JUnit 4 runner or Vintage dependency remains.
• At least the existing 45 classes and 286 tests are discovered.
• The complete suite passes against every supported IntelliJ Platform version.
• Test-count verification prevents silent test omission during migration.

References

• JetBrains UI Testing Support PR #537
• Current IntelliJ Platform plugin template
• IntelliJ Platform test framework types
• IntelliJ Platform Gradle Plugin FAQ
• Current IntelliJ JUnit 5 fixture guide