- Migrated all tests in org.eclipse.jface.tests to JUnit 5.
- Updated MANIFEST.MF to use org.junit.jupiter.api and removed JUnit 4.
- Replaced JUnit 4 Rules with JUnit 5 Extensions or @TempDir.
- Fixed assertion and assumption parameter order for JUnit 5.
- Removed unused JFaceActionRule.
- Replaced JUnit 3 AssertionFailedError with IllegalStateException in TestLazyModelContentProvider.