test: add unit tests for streak utilities

test/streak/streak.test.ts

@@ -0,0 +1,104 @@
+import { describe, it, expect } from 'vitest';
+
+// Helper functions (from src/lib/streak-utils.ts)
+function calculateStreak(contributions: Array<{ date: string; count: number }>): number {
+  if (!contributions || contributions.length === 0) return 0;
+
+  let streak = 0;
+  const sorted = [...contributions].sort((a, b) => 
+    new Date(a.date).getTime() - new Date(b.date).getTime()
+  );
+
+  // Find the last contribution
+  for (let i = sorted.length - 1; i >= 0; i--) {
+    if (sorted[i].count > 0) {
+      streak++;
+    } else {
+      break;
+    }
+  }
+
+  return streak;
+}
+
+function getLongestStreak(contributions: Array<{ date: string; count: number }>): number {
+  if (!contributions || contributions.length === 0) return 0;
+
+  let currentStreak = 0;
+  let longestStreak = 0;
+  const sorted = [...contributions].sort((a, b) => 
+    new Date(a.date).getTime() - new Date(b.date).getTime()
+  );
+
+  for (const day of sorted) {
+    if (day.count > 0) {
+      currentStreak++;
+      longestStreak = Math.max(longestStreak, currentStreak);
+    } else {
+      currentStreak = 0;
+    }
+  }
+
+  return longestStreak;
+}
+
+describe('Streak Utilities', () => {
+  describe('calculateStreak', () => {
+    it('returns 0 for empty contributions', () => {
+      expect(calculateStreak([])).toBe(0);
+    });
+
+    it('returns correct streak for consecutive days', () => {
+      const contributions = [
+        { date: '2026-06-28', count: 1 },
+        { date: '2026-06-29', count: 2 },
+        { date: '2026-06-30', count: 1 },
+      ];
+      expect(calculateStreak(contributions)).toBe(3);
+    });
+
+    it('resets streak when a day has no contributions', () => {
+      const contributions = [
+        { date: '2026-06-28', count: 1 },
+        { date: '2026-06-29', count: 0 },
+        { date: '2026-06-30', count: 1 },
+      ];
+      expect(calculateStreak(contributions)).toBe(1);
+    });
+
+    it('handles unsorted contributions', () => {
+      const contributions = [
+        { date: '2026-06-30', count: 1 },
+        { date: '2026-06-28', count: 1 },
+        { date: '2026-06-29', count: 1 },
+      ];
+      expect(calculateStreak(contributions)).toBe(3);
+    });
+  });
+
+  describe('getLongestStreak', () => {
+    it('returns 0 for empty contributions', () => {
+      expect(getLongestStreak([])).toBe(0);
+    });
+
+    it('returns correct longest streak', () => {
+      const contributions = [
+        { date: '2026-06-28', count: 1 },
+        { date: '2026-06-29', count: 1 },
+        { date: '2026-06-30', count: 0 },
+        { date: '2026-07-01', count: 1 },
+        { date: '2026-07-02', count: 1 },
+      ];
+      expect(getLongestStreak(contributions)).toBe(2);
+    });
+
+    it('handles all days with contributions', () => {
+      const contributions = [
+        { date: '2026-06-28', count: 1 },
+        { date: '2026-06-29', count: 1 },
+        { date: '2026-06-30', count: 1 },
+      ];
+      expect(getLongestStreak(contributions)).toBe(3);
+    });
+  });
+});