test(themes): add forest theme tests (JhaSourav07#2308) (JhaSourav07#3124)

## Description

Fixes JhaSourav07#2308

Created a dedicated unit test file `lib/svg/themes/forest.test.ts` to
verify the color variables and configuration of the `forest` theme, as
outlined in the issue.

### Implementation Steps Covered
- ✅ Imports the `themes` object from `lib/svg/themes.ts`
- ✅ Asserts the `forest` key exists
- ✅ Verifies `themes.forest.bg`, `themes.forest.text`, and
`themes.forest.accent` are valid 6-character hex strings (using regex)
- ✅ Generates a dummy SVG using `generateSVG` configured with the forest
theme and asserts the theme's hex colors appear in the output
- ✅ Ensures the contrast between `bg` and `text` meets WCAG AA
accessibility criteria (≥ 4.5:1)

### 6 Tests Added — All Passing ✅

1. ✅ **imports the themes object and asserts the forest key exists**
2. ✅ **verifies `themes.forest.bg` is a valid 6-character hex color**
3. ✅ **verifies `themes.forest.text` is a valid 6-character hex color**
4. ✅ **verifies `themes.forest.accent` is a valid 6-character hex
color**
5. ✅ **generates an SVG using the forest theme and asserts theme hex
colors appear in the output**
6. ✅ **ensures the contrast between forest bg and text is sufficient
(WCAG accessibility)**

**Test Summary:**
- Test Files: `1 passed (1)`
- Tests: `6 passed (6)`
- Command used: `npx vitest run lib/svg/themes/forest.test.ts`

## Pillar

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

## Visual Preview

_No visual changes — this PR adds test coverage only (no UI/SVG output
modifications)._

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally (`npx vitest run
lib/svg/themes/forest.test.ts` — all 6 tests pass).
- [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.
- [ ] 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).
- [ ] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

lib/svg/themes/forest.test.ts

@@ -0,0 +1,97 @@
+// lib/svg/themes/forest.test.ts
+import { describe, it, expect } from 'vitest';
+import { themes } from '../themes';
+import { generateSVG } from '../generator';
+import type { BadgeParams, ContributionCalendar, StreakStats } from '../../../types';
+
+describe('forest theme', () => {
+  const hexRegex = /^#[0-9a-f]{6}$/i;
+
+  const mockStats: StreakStats = {
+    currentStreak: 3,
+    longestStreak: 7,
+    totalContributions: 42,
+    todayDate: '2024-06-12',
+  };
+
+  const mockCalendar = {
+    weeks: [
+      {
+        contributionDays: [
+          { contributionCount: 0, date: '2024-06-10' },
+          { contributionCount: 4, date: '2024-06-11' },
+          { contributionCount: 9, date: '2024-06-12' },
+        ],
+      },
+    ],
+  } as ContributionCalendar;
+
+  it('imports the themes object and asserts the forest key exists', () => {
+    expect(themes).toHaveProperty('forest');
+    expect(themes.forest).toBeDefined();
+  });
+
+  it('verifies themes.forest.bg is a valid 6-character hex color', () => {
+    expect(`#${themes.forest.bg}`, 'forest bg is invalid').toMatch(hexRegex);
+  });
+
+  it('verifies themes.forest.text is a valid 6-character hex color', () => {
+    expect(`#${themes.forest.text}`, 'forest text is invalid').toMatch(hexRegex);
+  });
+
+  it('verifies themes.forest.accent is a valid 6-character hex color', () => {
+    expect(`#${themes.forest.accent}`, 'forest accent is invalid').toMatch(hexRegex);
+  });
+
+  it('generates an SVG using the forest theme and asserts theme hex colors appear in the output', () => {
+    const forest = themes.forest;
+
+    const svg = generateSVG(
+      mockStats,
+      {
+        user: 'tester',
+        bg: forest.bg,
+        text: forest.text,
+        accent: forest.accent,
+        speed: '8s',
+        scale: 'linear',
+      } as unknown as BadgeParams,
+      mockCalendar
+    );
+
+    expect(svg).toBeTypeOf('string');
+    expect(svg.length).toBeGreaterThan(0);
+    // The generator prepends '#' to the sanitized hex values
+    expect(svg).toContain(`#${forest.bg}`);
+    expect(svg).toContain(`#${forest.text}`);
+    expect(svg).toContain(`#${forest.accent}`);
+  });
+
+  it('ensures the contrast between forest bg and text is sufficient (WCAG accessibility)', () => {
+    const hexToRgb = (hex: string): [number, number, number] => {
+      const h = hex.replace('#', '');
+      return [
+        parseInt(h.substring(0, 2), 16),
+        parseInt(h.substring(2, 4), 16),
+        parseInt(h.substring(4, 6), 16),
+      ];
+    };
+
+    const luminance = ([r, g, b]: [number, number, number]): number => {
+      const a = [r, g, b].map((v) => {
+        const s = v / 255;
+        return s <= 0.03928 ? s / 12.92 : Math.pow((s + 0.055) / 1.055, 2.4);
+      });
+      return 0.2126 * a[0] + 0.7152 * a[1] + 0.0722 * a[2];
+    };
+
+    const bgLum = luminance(hexToRgb(themes.forest.bg));
+    const textLum = luminance(hexToRgb(themes.forest.text));
+    const lighter = Math.max(bgLum, textLum);
+    const darker = Math.min(bgLum, textLum);
+    const contrastRatio = (lighter + 0.05) / (darker + 0.05);
+
+    // WCAG AA requires at least 4.5:1 for normal text
+    expect(contrastRatio).toBeGreaterThanOrEqual(4.5);
+  });
+});