test(dashboard): add timezone normalization and boundary tests for DashboardClient (JhaSourav07#3613)

## Description

Fixes JhaSourav07#2530 

### What Changed
* **Timezone Boundary Tests
(`components/dashboard/DashboardClient.timezone-boundaries.test.tsx`):**
Added a new Vitest suite to verify system clock normalization, leap year
parsing, and Daylight Savings Time (DST) offsets.
* **Time Travel Mocks:** Implemented `vi.useFakeTimers()` to strictly
control the virtual environment's clock. This allows us to safely test
midnight crossovers and edge cases without flakey test runs.
* **Component Isolation:** Mocked heavy visual children (like
`ActivityLandscape` and `Heatmap`) to prevent JSDOM canvas crashes,
ensuring lightning-fast integration testing of the core date-parsing
logic.
* **Named Export Fixes:** Correctly mocked `PopularRepos` as a named
export and utilized `Parameters<typeof DashboardClient>` to resolve
React rendering crashes and strict TypeScript `any` linting errors in
the testing environment.

## Pillar

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

## Visual Preview
**N/A for test changes.

## 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): ...`).
- [x] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [x] 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/dashboard/DashboardClient.timezone-boundaries.test.tsx

@@ -0,0 +1,141 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import DashboardClient from './DashboardClient';
+import type { DashboardPeriod } from '@/utils/dashboardPeriod';
+
+// 1. Mock Next.js router to prevent crashes
+vi.mock('next/navigation', () => ({
+  useRouter: () => ({ replace: vi.fn() }),
+}));
+
+// 2. Isolate Date logic by mocking the heavy visual children
+vi.mock('./StatsCard', () => ({
+  default: ({ title, utcDate }: { title: string; utcDate: string }) => (
+    <div data-testid={`stats-card-${title.replace(/\s+/g, '-')}`} data-utc-date={utcDate}>
+      {title}
+    </div>
+  ),
+}));
+
+// Mocking the rest of the visual components as empty divs to prevent JSDOM Canvas errors
+vi.mock('./ProfileCard', () => ({ default: () => <div /> }));
+vi.mock('./Achievements', () => ({ default: () => <div /> }));
+vi.mock('./ActivityLandscape', () => ({ default: () => <div /> }));
+vi.mock('./LanguageChart', () => ({ default: () => <div /> }));
+vi.mock('./CommitClock', () => ({ default: () => <div /> }));
+vi.mock('./HistoricalTrendView', () => ({ default: () => <div /> }));
+vi.mock('./AIInsights', () => ({ default: () => <div /> }));
+vi.mock('./PopularRepos', () => ({ PopularRepos: () => <div /> }));
+vi.mock('./RepositoryGraph', () => ({ default: () => <div /> }));
+vi.mock('./Heatmap', () => ({ default: () => <div /> }));
+vi.mock('./RefreshButton', () => ({ default: () => <div /> }));
+
+// 3. Minimum mock data required to render the DashboardClient
+const mockPeriod = { label: 'Last Year' } as unknown as DashboardPeriod;
+const mockInitialData = {
+  profile: { name: 'TestUser', stats: { repositories: 10 } },
+  stats: { currentStreak: 5, peakStreak: 15, totalContributions: 100 },
+  languages: [],
+  activity: [{ date: '2026-06-03', count: 5, intensity: 3 }],
+  insights: [],
+  achievements: [],
+  commitClock: [{ day: 'Mon', commits: 10 }],
+  graphData: { nodes: [], links: [] },
+} as unknown as Parameters<typeof DashboardClient>[0]['initialData'];
+
+describe('DashboardClient - Timezone Normalization & Boundary Alignment', () => {
+  beforeEach(() => {
+    // Enable simulated timers so we can freely manipulate the system clock
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    // Restore the real system clock after every test
+    vi.useRealTimers();
+    vi.clearAllMocks();
+  });
+
+  // Test 1: Standard Timezone Boundaries (JST/EST to UTC)
+  it('mocks standard timezone settings (JST/EST) and calculates commits onto correct UTC dates', () => {
+    // Simulate Tokyo Time (JST) crossing midnight into June 4th (UTC is still June 3rd, 3:00 PM)
+    vi.setSystemTime(new Date('2026-06-03T15:00:00Z'));
+    const { rerender } = render(
+      <DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />
+    );
+
+    let streakCard = screen.getByTestId('stats-card-Current-Streak');
+    expect(streakCard.getAttribute('data-utc-date')).toBe('2026-06-03');
+
+    // Simulate New York Time (EST) early morning June 4th (UTC is June 4th, 12:00 PM)
+    vi.setSystemTime(new Date('2026-06-04T12:00:00Z'));
+    rerender(<DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />);
+
+    streakCard = screen.getByTestId('stats-card-Current-Streak');
+    expect(streakCard.getAttribute('data-utc-date')).toBe('2026-06-04');
+  });
+
+  // Test 2: Leap Year Alignment
+  it('verifies leap year boundaries parse without leaving gaps in calendar alignment', () => {
+    // Set time strictly to a Leap Year boundary
+    vi.setSystemTime(new Date('2024-02-29T12:00:00Z'));
+    render(<DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />);
+
+    const streakCard = screen.getByTestId('stats-card-Current-Streak');
+    // Ensure the dashboard doesn't accidentally roll over to March 1st
+    expect(streakCard.getAttribute('data-utc-date')).toBe('2024-02-29');
+  });
+
+  // Test 3: Daylight Savings Offsets
+  it('tests offsets around transition dates like Daylight Savings Time (DST)', () => {
+    // US Spring Forward happens at 2:00 AM in March.
+    // Testing 1:59 AM (Before shift)
+    vi.setSystemTime(new Date('2026-03-08T06:59:59Z')); // UTC equivalent
+    const { rerender } = render(
+      <DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />
+    );
+
+    let streakCard = screen.getByTestId('stats-card-Current-Streak');
+    expect(streakCard.getAttribute('data-utc-date')).toBe('2026-03-08');
+
+    // Testing 3:00 AM (After shift - skips 2:00 AM)
+    vi.setSystemTime(new Date('2026-03-08T08:00:00Z')); // UTC equivalent
+    rerender(<DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />);
+
+    streakCard = screen.getByTestId('stats-card-Current-Streak');
+    // The UTC date should remain rock-solid regardless of the local DST jump
+    expect(streakCard.getAttribute('data-utc-date')).toBe('2026-03-08');
+  });
+
+  // Test 4: Calendar Date Formatting
+  it('asserts calendar date format utility outputs match strictly YYYY-MM-DD expectations', () => {
+    // Pick a single digit month and day to ensure no missing zero-padding
+    vi.setSystemTime(new Date('2026-01-05T08:00:00Z'));
+    render(<DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />);
+
+    const streakCard = screen.getByTestId('stats-card-Current-Streak');
+    const dateStr = streakCard.getAttribute('data-utc-date') || '';
+
+    // Regex verifies it exactly matches YYYY-MM-DD format (e.g., 2026-01-05, not 2026-1-5)
+    expect(dateStr).toMatch(/^\d{4}-\d{2}-\d{2}$/);
+    expect(dateStr).toBe('2026-01-05');
+  });
+
+  // Test 5: End of Year Roll-over
+  it('verifies boundary alignment during the New Year crossover', () => {
+    // One second before New Year 2027 UTC
+    vi.setSystemTime(new Date('2026-12-31T23:59:59Z'));
+    const { rerender } = render(
+      <DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />
+    );
+
+    let streakCard = screen.getByTestId('stats-card-Current-Streak');
+    expect(streakCard.getAttribute('data-utc-date')).toBe('2026-12-31');
+
+    // Two seconds later... Happy New Year!
+    vi.setSystemTime(new Date('2027-01-01T00:00:01Z'));
+    rerender(<DashboardClient initialData={mockInitialData} username="test" period={mockPeriod} />);
+
+    streakCard = screen.getByTestId('stats-card-Current-Streak');
+    expect(streakCard.getAttribute('data-utc-date')).toBe('2027-01-01');
+  });
+});