chore: add testing harness and e2e scaffolding

[harley]

Summary

• add vitest configuration, testing dependencies, and shared chrome mocks
• create initial unit tests across options UI, shared utilities, background, and content script
• introduce Playwright extension harness with mocked ChatGPT flow and document the new commands

Testing

• pnpm test (fails: vitest binary unavailable in this offline environment)

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https://chatgpt.com/codex/tasks/task_b_68d762ba1010832ba001bbaa6714e09f

[gemini-code-assist]

Summary of Changes

Hello @harley, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the project's reliability and maintainability by establishing a comprehensive testing infrastructure. It introduces both unit testing with Vitest and end-to-end testing with Playwright, ensuring that core functionalities of the extension, from background processes to UI interactions and content rendering, are thoroughly validated. This foundational work will enable more confident development and prevent regressions in future changes.

Highlights

• Unit Testing with Vitest: Integrated Vitest as the primary unit testing framework, complete with configuration, dependencies, and a mocked Chrome API environment to enable isolated testing of extension components.
• Comprehensive Unit Test Coverage: Added initial unit tests for critical components including the background script, content script, options UI, and shared utility functions, ensuring core logic is validated.
• End-to-End Testing with Playwright: Introduced Playwright for robust end-to-end testing, featuring an extension harness and a mocked ChatGPT flow to validate the extension's behavior in a browser environment.
• Updated Documentation and Scripts: The README.md has been updated with new testing commands, and package.json now includes scripts for running unit, watch, coverage, and e2e tests, streamlining the testing workflow.

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[gemini-code-assist]

Code Review

This pull request does an excellent job of setting up a comprehensive testing harness for the extension, including unit tests with Vitest and end-to-end tests with Playwright. The new test files are well-structured, and the mocking for the chrome API is robust. The configuration files for testing tools are also set up correctly.

I've made a few minor suggestions to improve dependency management, fix a small issue in a test expectation, and make the Playwright configuration more CI-friendly. Overall, this is a fantastic contribution that significantly improves the project's quality and maintainability.

[gemini-code-assist]

You have both happy-dom and jsdom as dev dependencies. Your Vitest configuration (vitest.config.ts) is set to use happy-dom as the test environment. Since jsdom is not being used by Vitest and doesn't seem to be a dependency for other testing libraries you've added, you can remove it to keep dependencies clean.

[harley]

@codex fix this

[chatgpt-codex-connector]

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