Add unit tests for utils and module pure functions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/unit/module/shortScaleNumber.test.js

@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest';
+import shortScaleNumber from '@/module/shortScaleNumber.js';
+
+describe('shortScaleNumber', () => {
+  it('returns small numbers without abbreviation', () => {
+    expect(shortScaleNumber(1).trim()).toBe('1');
+    expect(shortScaleNumber(999).trim()).toBe('999');
+  });
+
+  it('abbreviates thousands as k', () => {
+    expect(shortScaleNumber(1000).trim()).toBe('1k');
+    expect(shortScaleNumber(1500).trim()).toBe('1.5k');
+  });
+
+  it('abbreviates millions as m', () => {
+    expect(shortScaleNumber(1000000).trim()).toBe('1m');
+  });
+
+  it('abbreviates billions as b', () => {
+    expect(shortScaleNumber(1000000000).trim()).toBe('1b');
+  });
+
+  it('abbreviates trillions as t', () => {
+    expect(shortScaleNumber(1000000000000).trim())
+      .toBe('1t');
+  });
+
+  it('rounds up using Math.ceil', () => {
+    // 1234 -> 1.234k -> ceil(12.34)/10 = 1.3k
+    expect(shortScaleNumber(1234).trim()).toBe('1.3k');
+  });
+
+  it('handles zero', () => {
+    expect(shortScaleNumber(0).trim()).toBe('0');
+  });
+});