fix(employees): preserve age across birthday boundaries

web/tests/employee-management-age.test.mjs

@@ -0,0 +1,44 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+
+import {
+  calculateAgeFromDate,
+  calculateBirthDateFromAge,
+  isValidIsoDate
+} from '../src/views/scripts/employeeManagementModel.js'
+
+test('根据年龄反算未到生日的出生年份不会少一年', () => {
+  const referenceDate = new Date('2026-07-18T00:00:00')
+  const birthDate = calculateBirthDateFromAge('30', '1990-12-31', referenceDate)
+
+  assert.equal(birthDate, '1995-12-31')
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '30')
+})
+
+test('根据年龄反算已过生日的出生年份保持当年差值', () => {
+  const referenceDate = new Date('2026-07-18T00:00:00')
+  const birthDate = calculateBirthDateFromAge('30', '1990-01-01', referenceDate)
+
+  assert.equal(birthDate, '1996-01-01')
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '30')
+})
+
+test('零岁且生日月日尚未到来时不会生成未来出生日期', () => {
+  const referenceDate = new Date('2026-07-18T00:00:00')
+  const birthDate = calculateBirthDateFromAge('0', '2000-12-31', referenceDate)
+
+  assert.equal(birthDate, '2025-12-31')
+  assert.equal(isValidIsoDate(birthDate), true)
+  assert.equal(new Date(`${birthDate}T00:00:00`) <= referenceDate, true)
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '0')
+})
+
+test('闰日生日跨非闰年时使用二月二十八日并保持年龄回算一致', () => {
+  const referenceDate = new Date('2024-03-01T00:00:00')
+  const birthDate = calculateBirthDateFromAge('23', '2000-02-29', referenceDate)
+
+  assert.equal(birthDate, '2001-02-28')
+  assert.equal(isValidIsoDate(birthDate), true)
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '23')
+  assert.equal(calculateAgeFromDate('2000-02-29', new Date('2023-02-28T00:00:00')), '23')
+})