Add unit tests for utils and module pure functions

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

tests/unit/module/abbreviateNumber.test.js

@@ -0,0 +1,46 @@
+import { describe, it, expect } from 'vitest';
+import abbreviateNumber from '@/module/abbreviateNumber.js';
+
+describe('abbreviateNumber', () => {
+  it('returns "0" for 0 seconds', () => {
+    expect(abbreviateNumber(0)).toBe('0');
+  });
+
+  it('returns seconds only when < 60', () => {
+    expect(abbreviateNumber(45).trim()).toBe('45s');
+  });
+
+  it('returns minutes and seconds', () => {
+    // 2m 30s = 150s
+    expect(abbreviateNumber(150).trim()).toBe('2m 30s');
+  });
+
+  it('returns hours, minutes, and seconds', () => {
+    // 1h 1m 1s = 3661s
+    expect(abbreviateNumber(3661).trim()).toBe('1h 1m 1s');
+  });
+
+  it('returns days, hours, minutes, and seconds', () => {
+    // 1d 2h 3m 4s = 93784s
+    expect(abbreviateNumber(93784).trim())
+      .toBe('1d 2h 3m 4s');
+  });
+
+  it('handles exact day boundary', () => {
+    // 1d = 86400s
+    expect(abbreviateNumber(86400).trim()).toBe('1d');
+  });
+
+  it('handles exact hour boundary', () => {
+    // 1h = 3600s
+    expect(abbreviateNumber(3600).trim()).toBe('1h');
+  });
+
+  it('handles string input by parsing as int', () => {
+    expect(abbreviateNumber('150').trim()).toBe('2m 30s');
+  });
+
+  it('handles NaN input', () => {
+    expect(abbreviateNumber('abc').trim()).toBe('');
+  });
+});