test: add price formatting tests

__tests__/formatting.test.ts

@@ -0,0 +1,49 @@
+import { describe, it, expect, test, jest, mock, beforeEach } from "bun:test";
+import { formatPrice } from '../src/content/utils/formatting';
+import { $T } from '../src/content/utils/localization';
+
+mock.module('../src/content/utils/localization', () => ({
+    $T: mock((str) => str)
+}));
+
+mock.module('../src/content/config', () => ({
+    conversion_ref_usd: 0.05 // Mock conversion rate
+}))
+
+describe('formatPrice', () => {
+    beforeEach(() => {
+      jest.clearAllMocks()
+    });
+
+    test('formats price with keys and metal', () => {
+        expect(formatPrice(2, 10, 50)).toBe('2.2 keys (US$5.50)');
+        expect($T).toHaveBeenCalledWith('%@ keys');
+    });
+
+    test('formats price with metal only', () => {
+        expect(formatPrice(0, 15.75, 50)).toBe('15.75 ref (US$0.79)');
+    });
+
+    test('formats price with metal only and whole number', () => {
+        expect(formatPrice(0, 3, 50)).toBe('3 ref (US$0.16)');
+    });
+
+    test('uses singular key form', () => {
+        expect(formatPrice(1, 0, 50)).toBe('1 key (US$2.50)');
+        expect($T).toHaveBeenCalledWith('%@ key');
+    });
+
+    test('rounds USD up to nearest cent', () => {
+        expect(formatPrice(3, 7.33, 35)).toBe('3.21 keys (US$5.62)');  // (3*35 +7.33)*0.05 = 5.6165  → 5.62
+    });
+
+    test('handles different locale formatting', () => {
+        expect(formatPrice(2, 10, 50, 'de')).toMatch(/2,2 keys \(US\$5,50\)/);
+        expect(formatPrice(0, 15.75, 50, 'de')).toMatch(/15,75 ref \(US\$0,79\)/);
+    });
+
+    test('handles zero values', () => {
+        expect(formatPrice(0, 0, 50)).toBe('0 ref (US$0.00)');
+        expect(formatPrice(0, 0, 50, 'de')).toMatch(/0 ref \(US\$0,00\)/);
+    });
+});