Incremental Migration to Stencil Vitest Runner

[janivo]

Code Smells / Technical Debt

With the release of Stencil 4.43 (and refined in subsequent versions), a new Vitest-based test runner was introduced. The current Jest-based runner is marked for deprecation in the upcoming major version of Stencil.

Currently, our test suite relies on the legacy Jest integration. Staying on the legacy runner will prevent us from upgrading to future Stencil versions and misses out on the performance benefits and modern API support provided by Vitest. However, initial testing on ino-control-item suggests that the new runner still exhibits some instabilities, making a "big bang" migration risky for our CI stability.

Proposed Technical Approach

We will adopt a hybrid testing strategy to migrate packages/elements incrementally.

Infrastructure Setup

• Integrate @stencil/vitest and vitest into the packages/elements workspace.
• Configure stencil.config.ts to support the Vitest output target/testing configuration.
• Update package.json scripts to support running both Jest and Vitest suites.

File Naming Convention

• Keep existing legacy tests as *.spec.ts (Jest).
• Implement new or migrated tests as *.vitest-spec.ts. This allows the runners to target specific files without overlap.

Incremental Migration Steps

• Finalize the migration for ino-control-item as the first official component on Vitest.
• All newly created components must use the .vitest-spec.ts format.
• Whenever an existing component requires significant logic changes or has a failing Jest test (as seen with ino-control-item), that component's suite should be migrated to Vitest.

Compatibility Mapping

• Follow the Stencil Vitest Migration Guide.
• Replace newSpecPage and newE2EPage with the updated Vitest testing utilities.
• Update matchers from jest globals to vitest assertions.

Additional Context

• Migration Guide: https://stenciljs.com/docs/testing-vitest-migration
• The hybrid approach ensures that components that prove difficult to migrate due to runner bugs stay stable on Jest until the Stencil Vitest runner matures further.