Introduction

This week, I embark on a journey of Testing, which is one of the interesting aspects of Programming. Sometimes you will think you’ve got everything covered, but no, there are lots of loopholes than you think. So, for this Testing, I went with Vitest.

Why Vitest?

Automated testing was the focus for this lab, so I needed a framework that matched the TypeScript-first nature of the project. I compared Jest and Vitest, and ultimately went with Vitest (docs) because:

• It runs tests directly against modern JS/TS without extra transpilation glue.
• Watch mode and focused test runs are built-in (vitest --watch, vitest run --filter ...).
• Coverage via the @vitest/coverage-istanbul plugin is a single flag away.
• The CLI feels familiar coming from Jest, so there was very little learning curve.

The only snag was peer dependency alignment: Vitest 4 expects @types/node ≥ 20, while the project was still on 14. Bumping the type definitions resolved the install conflict without touching runtime Node requirements.

Framework Setup

Getting Vitest wired in was straightforward:

1. Installed the packages: npm i -D vitest @vitest/coverage-istanbul.
2. Added a tiny vitest.config.ts to ensure we use the Node environment and to configure coverage reporters.
3. Replaced the placeholder npm test script with vitest, added helpers for single runs and watch mode, and exposed coverage via npm run test:coverage.
4. Documented the commands in README.md so anyone on the team can run the right workflow quickly.

At this point, npm test ran (and passed) an empty suite—mission accomplished for Step 1.

Building the Test Suite

I started small, writing the very first unit tests around the easiest pure functions:

• calculateTokens, formatOutput, and truncateContent in src/utils.ts.

These covered happy paths as well as a couple of edge cases (rounding behaviour and truncation markers). Once that foundation was in place, I layered on additional suites for other parts of the codebase:

1. Repository statistics – verified that RepositoryStatistics correctly tracks totals, token counts, directory sets, averages, limit checks, and reset behaviour.
2. Summarizer – confirmed that imports, exports, and function metadata are captured, and that the formatted output includes the right cues for summary mode. While writing these tests I discovered that async exports weren’t being picked up; fixing the regex so it recognises export async function resulted in the first “aha!” bug found by testing.
3. Packager – used Vitest’s filesystem-friendly test runner to spin up temporary directories, mock Git metadata, and exercise the higher-level workflow. These tests proved that the CLI can:

• Analyse files and accumulate RepoInfo.
• Generate summary-mode output without throwing.
• Respect maxFileSize limits and skip oversized files.

Altogether the suite now has 12 tests, touching everything from helper utilities to integration-style Packager runs.

Running Focused Tests (Step 4)

One pain point with larger projects is rerunning the entire suite while iterating on a single failing test. Vitest’s command-line options make this easy:

• npm run test:watch keeps tests hot-reloading as files change.
• npm run test:file -- src/packager.test.ts scopes execution to one file.
• npm run test:run -- --filter "Packager" is handy when I just want the Packager suite.

These scripts, together with the README notes, satisfied Step 4’s “test runner improvements” goal.

Optional Coverage

Although not strictly required, the coverage command (npm run test:coverage) is ready to go thanks to the Istanbul plugin. Running it highlights remaining gaps—logger helpers and some CLI validation branches are still untested—which gives me a roadmap for future edge-case coverage.

Lessons Learned

• Targeted unit tests surface subtle bugs. Without the summarizer tests, I might never have noticed async exports disappearing.
• Type alignment matters. Even small dependencies like @types/node can block installation; upgrading them early avoids wasted time.
• Integration-style tests add confidence fast. The Packager suite spins up temporary workspaces, letting me verify real workflows without touching the actual filesystem.

Overall, this lab reinforced that investing in a clean testing setup unlocks safer refactoring and faster iteration. The Repository Context Packager now has a reliable safety net, and I’m more confident shipping improvements in the future.