No testing framework present — blocks adding automated tests #25

Summary

The project currently has no testing framework or test suite. package.json defines only compile, watch, and vscode:prepublish scripts, there's no test runner in devDependencies, and there are no test files anywhere in the repo.

This makes it impossible to add automated tests alongside bug fixes and features, which is standard best practice — regressions (like a stale status-bar value, or pricing/aggregation miscalculations) currently can only be caught by manual F5 debugging in the Extension Development Host.

Why it matters

• Much of the logic is pure and highly testable in isolation: cost/pricing calculation (pricing.ts), data aggregation (daily/weekly/monthly/all-time in dataLoader.ts), quota-window handling (statusBar.ts), and i18n formatting (i18n.ts).
• Without tests, every change risks silent regressions and reviewers have no automated signal.
• A test suite would also enable CI to gate PRs.

Proposal

Add a lightweight test setup with minimal new dependencies. A couple of viable options:

• Node's built-in test runner (node:test + node:assert) — zero new dependencies, run compiled output via node --test out/test/. Best for the pure logic modules that don't import the vscode API.
• @vscode/test-electron + Mocha — the official VS Code extension testing approach, needed for anything that touches the live vscode API.

A pragmatic split is to extract pure logic into dependency-free modules and cover those with node:test, reserving the heavier electron-based harness for genuinely vscode-coupled code. Adding a test npm script and a CI workflow to run it on PRs would round it out.

Happy to open a PR setting this up if it'd be welcome.