diff --git a/test/streak/streak.test.ts b/test/streak/streak.test.ts
new file mode 100644
index 000000000..dc772c449
--- /dev/null
+++ b/test/streak/streak.test.ts
@@ -0,0 +1,145 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { calculateCurrentStreak, calculateLongestStreak } from '@/lib/streak-utils';
+
+describe('Streak Utilities', () => {
+  describe('calculateCurrentStreak', () => {
+    it('returns 0 for empty contributions', () => {
+      expect(calculateCurrentStreak([])).toBe(0);
+    });
+
+    it('returns correct streak for consecutive days ending today', () => {
+      const today = new Date();
+      const yesterday = new Date(today);
+      yesterday.setDate(yesterday.getDate() - 1);
+      const twoDaysAgo = new Date(today);
+      twoDaysAgo.setDate(twoDaysAgo.getDate() - 2);
+
+      const dates = [
+        twoDaysAgo.toISOString().split('T')[0],
+        yesterday.toISOString().split('T')[0],
+        today.toISOString().split('T')[0],
+      ];
+      expect(calculateCurrentStreak(dates)).toBe(3);
+    });
+
+    it('returns 0 when last activity was more than 1 day ago', () => {
+      const today = new Date();
+      const threeDaysAgo = new Date(today);
+      threeDaysAgo.setDate(threeDaysAgo.getDate() - 3);
+
+      const dates = [
+        threeDaysAgo.toISOString().split('T')[0],
+      ];
+      expect(calculateCurrentStreak(dates)).toBe(0);
+    });
+
+    it('handles Date objects', () => {
+      const today = new Date();
+      const yesterday = new Date(today);
+      yesterday.setDate(yesterday.getDate() - 1);
+
+      const dates = [yesterday, today];
+      expect(calculateCurrentStreak(dates)).toBe(2);
+    });
+
+    it('handles unsorted dates', () => {
+      const today = new Date();
+      const yesterday = new Date(today);
+      yesterday.setDate(yesterday.getDate() - 1);
+      const twoDaysAgo = new Date(today);
+      twoDaysAgo.setDate(twoDaysAgo.getDate() - 2);
+
+      const dates = [
+        today.toISOString().split('T')[0],
+        twoDaysAgo.toISOString().split('T')[0],
+        yesterday.toISOString().split('T')[0],
+      ];
+      expect(calculateCurrentStreak(dates)).toBe(3);
+    });
+
+    it('handles duplicate dates', () => {
+      const today = new Date();
+      const yesterday = new Date(today);
+      yesterday.setDate(yesterday.getDate() - 1);
+
+      const dates = [
+        today.toISOString().split('T')[0],
+        today.toISOString().split('T')[0],
+        yesterday.toISOString().split('T')[0],
+      ];
+      expect(calculateCurrentStreak(dates)).toBe(2);
+    });
+
+    it('returns 0 for invalid dates', () => {
+      const dates = ['invalid-date', '2024-01-01'];
+      expect(calculateCurrentStreak(dates)).toBe(0);
+    });
+  });
+
+  describe('calculateLongestStreak', () => {
+    it('returns 0 for empty contributions', () => {
+      expect(calculateLongestStreak([])).toBe(0);
+    });
+
+    it('returns correct longest streak', () => {
+      const dates = [
+        '2026-06-28',
+        '2026-06-29',
+        '2026-06-30',
+        '2026-07-02',
+        '2026-07-03',
+      ];
+      expect(calculateLongestStreak(dates)).toBe(3);
+    });
+
+    it('handles single-day streaks', () => {
+      const dates = ['2026-06-28', '2026-06-30', '2026-07-02'];
+      expect(calculateLongestStreak(dates)).toBe(1);
+    });
+
+    it('handles all days with contributions', () => {
+      const dates = [
+        '2026-06-28',
+        '2026-06-29',
+        '2026-06-30',
+        '2026-07-01',
+        '2026-07-02',
+      ];
+      expect(calculateLongestStreak(dates)).toBe(5);
+    });
+
+    it('handles Date objects', () => {
+      const dates = [
+        new Date('2026-06-28'),
+        new Date('2026-06-29'),
+        new Date('2026-06-30'),
+      ];
+      expect(calculateLongestStreak(dates)).toBe(3);
+    });
+
+    it('handles unsorted dates', () => {
+      const dates = [
+        '2026-06-30',
+        '2026-06-28',
+        '2026-06-29',
+        '2026-07-01',
+      ];
+      expect(calculateLongestStreak(dates)).toBe(4);
+    });
+
+    it('handles duplicate dates', () => {
+      const dates = [
+        '2026-06-28',
+        '2026-06-28',
+        '2026-06-29',
+        '2026-06-30',
+      ];
+      expect(calculateLongestStreak(dates)).toBe(3);
+    });
+
+    it('ignores invalid dates', () => {
+      const dates = ['invalid-date', '2026-06-28', '2026-06-29'];
+      expect(calculateLongestStreak(dates)).toBe(2);
+    });
+  });
+});
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