test(calculate): verify streak formulas for only weekday contributions timeline (JhaSourav07#1475) (JhaSourav07#2026)

## Description

This PR adds a specific Vitest test case to `lib/calculate.test.ts` to
simulate a contribution timeline containing exclusively Monday through
Friday commits. This test explicitly proves the off-by-one error where
the current streak is prematurely broken across weekend boundaries.

Fixes JhaSourav07#1475

## Pillar
- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview
N/A — This PR only adds a unit test for backend calculation logic. No
visual SVG changes were made.

## Checklist before requesting a review:
- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [ ] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have starred the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [ ] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

components/DiscordButton.tsx

@@ -1,5 +1,4 @@
 'use client';
-
 import { useRef, useState, useEffect } from 'react';
 import { motion } from 'framer-motion';
 import gsap from 'gsap';

lib/calculate.test.ts

@@ -322,6 +322,33 @@ describe('calculateStreak', () => {
     expect(result.totalContributions).toBe(1);
     expect(result.longestStreak).toBe(1);
   });
+  it.fails('simulates a streak containing ONLY Monday through Friday commits (Issue #1475)', () => {
+    // buildCalendar assumes index 0 is a Monday.
+    // Days in a week: Mon(1), Tue(1), Wed(1), Thu(1), Fri(1), Sat(0), Sun(0)
+    // We will simulate 3 full weeks of this pattern.
+    const calendar = buildCalendar([
+      // Week 1
+      1, 1, 1, 1, 1, 0, 0,
+      // Week 2
+      1, 1, 1, 1, 1, 0, 0,
+      // Week 3
+      1, 1, 1, 1, 1, 0, 0,
+    ]);
+
+    // Evaluate the streak on the final Sunday of the calendar (index 20).
+    // Because the logic currently has an off-by-one bug when handling weekends,
+    // the test asserts what the math *should* output if weekend bridging is working correctly.
+    const result = calculateStreak(
+      calendar,
+      'UTC',
+      new Date('2024-01-21T12:00:00Z') // The date of the 3rd Sunday
+    );
+
+    // If weekend gaps are bridged properly, all 15 weekdays form a continuous streak.
+    expect(result.currentStreak).toBe(15);
+    expect(result.longestStreak).toBe(15);
+    expect(result.totalContributions).toBe(15);
+  });
 
   it('does not walk past the start of a 1-day calendar when grace is larger than the available days', () => {
     const calendar = buildCalendar([1]);