test: add unit tests for lib/format-date.ts

[adarshtiwari908]

Closes #326

Added unit tests for lib/format-date.ts covering 5 cases: standard date format, start of month, midnight timestamp, single-digit day, and end of year.

Checklist

• npm run lint
• npx tsc --noEmit
• npm run test:run
• npm run build

Summary by CodeRabbit

• Tests
  • Expanded test coverage for date formatting functionality with additional scenarios.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds a new test suite for the formatDate utility function, covering five scenarios: standard date/time formatting, start-of-month boundaries, midnight timestamps, single-digit day formatting, and end-of-year dates. Each test case asserts against the expected formatted string output.

Changes

formatDate test coverage

Layer / File(s)	Summary
formatDate test cases __tests__/lib/format-date.test.ts	Five Vitest test cases validate formatDate output for standard dates, month and day boundaries, midnight, single-digit day, and year-end timestamps, locking in current behavior.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related issues

• #326: This PR directly addresses the objective to add unit tests for lib/format-date.ts by creating the test file with all five required test cases (fixed UTC date, start-of-month, midnight, single-digit day, and end-of-year).

Poem

🐰 A date in the format, so clean and so bright,
Five tests now ensure it's perfectly right,
From month-start to midnight, year's end to the day,
The formatDate function won't lead us astray! 📅✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title clearly and concisely describes the main change: adding unit tests for the formatDate module.
Linked Issues check	✅ Passed	The PR adds comprehensive unit tests for formatDate covering all five required cases: fixed UTC date, start of month, midnight, single-digit day, and end of year as specified in issue #326.
Out of Scope Changes check	✅ Passed	All changes are within scope—only test file additions; no modifications to formatDate.ts or other library code outside the test requirements.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description check	✅ Passed	The pull request description includes all required sections from the template: a clear description of changes, a type of change identifier (implicitly test/documentation), and a completed checklist confirming all build/test steps pass.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@__tests__/lib/format-date.test.ts`:
- Line 6: The test creates a local-time Date with new Date(2024, 0, 15, 15, 45)
which can be non-deterministic across environments; change the construction to
use UTC by replacing that line with new Date(Date.UTC(2024, 0, 15, 15, 45))
(locate the const date in __tests__/lib/format-date.test.ts) so the test uses a
deterministic UTC timestamp.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 415accf6-26e1-4714-b850-bb50c8f53583

📥 Commits

Reviewing files that changed from the base of the PR and between b0f98bb and 3446b05.

📒 Files selected for processing (1)

• __tests__/lib/format-date.test.ts

[coderabbitai]

⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Use UTC date construction for deterministic test behavior.

Line 6 should use Date.UTC(...) (as requested in the issue objective) to avoid environment-dependent drift in date creation semantics.

Suggested fix

-    const date = new Date(2024, 0, 15, 15, 45);
+    const date = new Date(Date.UTC(2024, 0, 15, 15, 45));

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	const date = new Date(2024, 0, 15, 15, 45);
	const date = new Date(Date.UTC(2024, 0, 15, 15, 45));

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@__tests__/lib/format-date.test.ts` at line 6, The test creates a local-time
Date with new Date(2024, 0, 15, 15, 45) which can be non-deterministic across
environments; change the construction to use UTC by replacing that line with new
Date(Date.UTC(2024, 0, 15, 15, 45)) (locate the const date in
__tests__/lib/format-date.test.ts) so the test uses a deterministic UTC
timestamp.