test: 完善测试覆盖，新增 121 个测试用例

src/utils/billing.test.ts

@@ -3,9 +3,148 @@ import {
   DEFAULT_MONTHLY_PRICE_FACTOR,
   getAnnualSavings,
   getBillingOptions,
+  parseBillingMonths,
   resolveBillingPlan,
+  resolveMonthlyPrice,
+  resolveMonthlyPriceFactor,
 } from './billing';
 
+// ─── resolveMonthlyPriceFactor ──────────────────────────────────────
+
+describe('resolveMonthlyPriceFactor', () => {
+  test('returns default factor when no value provided', () => {
+    expect(resolveMonthlyPriceFactor()).toBe(DEFAULT_MONTHLY_PRICE_FACTOR);
+  });
+
+  test('returns default factor for undefined', () => {
+    expect(resolveMonthlyPriceFactor(undefined)).toBe(
+      DEFAULT_MONTHLY_PRICE_FACTOR,
+    );
+  });
+
+  test('returns default factor for 0', () => {
+    expect(resolveMonthlyPriceFactor(0)).toBe(DEFAULT_MONTHLY_PRICE_FACTOR);
+  });
+
+  test('returns default factor for negative number', () => {
+    expect(resolveMonthlyPriceFactor(-5)).toBe(DEFAULT_MONTHLY_PRICE_FACTOR);
+  });
+
+  test('returns default factor for NaN', () => {
+    expect(resolveMonthlyPriceFactor(NaN)).toBe(DEFAULT_MONTHLY_PRICE_FACTOR);
+  });
+
+  test('returns default factor for Infinity', () => {
+    expect(resolveMonthlyPriceFactor(Infinity)).toBe(
+      DEFAULT_MONTHLY_PRICE_FACTOR,
+    );
+  });
+
+  test('returns default factor for string', () => {
+    expect(resolveMonthlyPriceFactor('abc')).toBe(
+      DEFAULT_MONTHLY_PRICE_FACTOR,
+    );
+  });
+
+  test('returns custom factor for valid positive number', () => {
+    expect(resolveMonthlyPriceFactor(10)).toBe(10);
+  });
+
+  test('returns custom factor for decimal', () => {
+    expect(resolveMonthlyPriceFactor(8.5)).toBe(8.5);
+  });
+});
+
+// ─── resolveMonthlyPrice ────────────────────────────────────────────
+
+describe('resolveMonthlyPrice', () => {
+  test('divides annual price by default factor', () => {
+    expect(resolveMonthlyPrice(800)).toBe(100);
+  });
+
+  test('divides annual price by custom factor', () => {
+    expect(resolveMonthlyPrice(1000, 10)).toBe(100);
+  });
+
+  test('rounds to 2 decimal places', () => {
+    expect(resolveMonthlyPrice(100, 3)).toBe(33.33);
+  });
+
+  test('handles zero annual price', () => {
+    expect(resolveMonthlyPrice(0)).toBe(0);
+  });
+
+  test('handles large values', () => {
+    expect(resolveMonthlyPrice(120000, 12)).toBe(10000);
+  });
+
+  test('rounds correctly at boundary', () => {
+    expect(resolveMonthlyPrice(100)).toBe(12.5);
+  });
+
+  test('handles rounding edge case with EPSILON', () => {
+    expect(resolveMonthlyPrice(1, 3)).toBe(0.33);
+  });
+});
+
+// ─── parseBillingMonths ─────────────────────────────────────────────
+
+describe('parseBillingMonths', () => {
+  test('parses valid number', () => {
+    expect(parseBillingMonths(6)).toBe(6);
+  });
+
+  test('parses numeric string', () => {
+    expect(parseBillingMonths('3')).toBe(3);
+  });
+
+  test('truncates decimal', () => {
+    expect(parseBillingMonths(3.7)).toBe(3);
+  });
+
+  test('truncates decimal string', () => {
+    expect(parseBillingMonths('5.9')).toBe(5);
+  });
+
+  test('returns fallback for 0', () => {
+    expect(parseBillingMonths(0)).toBe(1);
+  });
+
+  test('returns fallback for negative', () => {
+    expect(parseBillingMonths(-1)).toBe(1);
+  });
+
+  test('returns fallback for NaN', () => {
+    expect(parseBillingMonths(NaN)).toBe(1);
+  });
+
+  test('returns fallback for Infinity', () => {
+    expect(parseBillingMonths(Infinity)).toBe(1);
+  });
+
+  test('returns fallback for non-numeric string', () => {
+    expect(parseBillingMonths('abc')).toBe(1);
+  });
+
+  test('returns custom fallback', () => {
+    expect(parseBillingMonths('abc', 12)).toBe(12);
+  });
+
+  test('returns default fallback for null', () => {
+    expect(parseBillingMonths(null)).toBe(1);
+  });
+
+  test('returns default fallback for undefined', () => {
+    expect(parseBillingMonths(undefined)).toBe(1);
+  });
+
+  test('returns fallback for empty string', () => {
+    expect(parseBillingMonths('')).toBe(1);
+  });
+});
+
+// ─── resolveBillingPlan (expanded) ──────────────────────────────────
+
 describe('resolveBillingPlan', () => {
   test('uses annual price divided by the default factor for one month', () => {
     const plan = resolveBillingPlan(800, 1, DEFAULT_MONTHLY_PRICE_FACTOR);
@@ -27,8 +166,59 @@ describe('resolveBillingPlan', () => {
     expect(plan.billingCycle).toBe('year');
     expect(plan.switchedToAnnual).toBe(true);
   });
+
+  test('defaults to 12 months when no months specified', () => {
+    const plan = resolveBillingPlan(800);
+    expect(plan.billingMonths).toBe(12);
+    expect(plan.billingCycle).toBe('year');
+    expect(plan.switchedToAnnual).toBe(true);
+  });
+
+  test('throws for months less than 1 after parsing', () => {
+    expect(() =>
+      resolveBillingPlan(800, 0, DEFAULT_MONTHLY_PRICE_FACTOR),
+    ).toThrow('Billing months must be a positive integer');
+  });
+
+  test('stores the monthly price factor in the plan', () => {
+    const plan = resolveBillingPlan(800, 1, 10);
+    expect(plan.monthlyPriceFactor).toBe(10);
+  });
+
+  test('calculates correct amount for 3 months', () => {
+    const plan = resolveBillingPlan(800, 3, DEFAULT_MONTHLY_PRICE_FACTOR);
+    expect(plan.amount).toBe(300);
+    expect(plan.billingCycle).toBe('month');
+    expect(plan.requestedMonths).toBe(3);
+    expect(plan.billingMonths).toBe(3);
+  });
+
+  test('handles zero annual price gracefully', () => {
+    const plan = resolveBillingPlan(0, 1, DEFAULT_MONTHLY_PRICE_FACTOR);
+    expect(plan.amount).toBe(0);
+    expect(plan.switchedToAnnual).toBe(false);
+    expect(plan.billingCycle).toBe('month');
+  });
+
+  test('handles custom monthly price factor', () => {
+    const plan = resolveBillingPlan(1200, 6, 10);
+    expect(plan.monthlyPrice).toBe(120);
+    expect(plan.amount).toBe(720);
+    expect(plan.billingCycle).toBe('month');
+
+    const plan2 = resolveBillingPlan(1200, 10, 10);
+    expect(plan2.switchedToAnnual).toBe(true);
+    expect(plan2.billingCycle).toBe('year');
+  });
+
+  test('requestedMonths is preserved in output', () => {
+    const plan = resolveBillingPlan(800, 5, DEFAULT_MONTHLY_PRICE_FACTOR);
+    expect(plan.requestedMonths).toBe(5);
+  });
 });
 
+// ─── getAnnualSavings (expanded) ────────────────────────────────────
+
 describe('getAnnualSavings', () => {
   test('returns annual savings compared with paying monthly', () => {
     const plan = resolveBillingPlan(800, 12, DEFAULT_MONTHLY_PRICE_FACTOR);
@@ -47,8 +237,35 @@ describe('getAnnualSavings', () => {
     expect(savings.percent).toBe(0);
     expect(savings.discount).toBe(0);
   });
+
+  test('returns zero savings when annual price equals monthly total', () => {
+    const plan = {
+      amount: 1200,
+      billingCycle: 'year' as const,
+      billingMonths: 12,
+      monthlyPrice: 100,
+    };
+    const savings = getAnnualSavings(plan);
+    expect(savings.amount).toBe(0);
+    expect(savings.percent).toBe(0);
+  });
+
+  test('returns zero for zero amount plan', () => {
+    const plan = {
+      amount: 0,
+      billingCycle: 'year' as const,
+      billingMonths: 12,
+      monthlyPrice: 0,
+    };
+    const savings = getAnnualSavings(plan);
+    expect(savings.amount).toBe(0);
+    expect(savings.percent).toBe(0);
+    expect(savings.discount).toBe(0);
+  });
 });
 
+// ─── getBillingOptions (expanded) ───────────────────────────────────
+
 describe('getBillingOptions', () => {
   test('removes month counts that would use annual billing', () => {
     const options = getBillingOptions({
@@ -72,4 +289,73 @@ describe('getBillingOptions', () => {
       JSON.stringify([1, 2, 3, 4, 5, 6, 7, 8, 9, 12]),
     );
   });
+
+  test('always includes annual option as last item', () => {
+    const options = getBillingOptions({
+      annualPrice: 2400,
+      monthlyPriceFactor: 8,
+    });
+
+    const last = options.at(-1)!;
+    expect(last.billingCycle).toBe('year');
+    expect(last.value).toBe(12);
+  });
+
+  test('all monthly options have billingCycle month', () => {
+    const options = getBillingOptions({
+      annualPrice: 800,
+      monthlyPriceFactor: 8,
+    });
+
+    for (const opt of options.slice(0, -1)) {
+      expect(opt.billingCycle).toBe('month');
+    }
+  });
+
+  test('options are ordered by value ascending', () => {
+    const options = getBillingOptions({
+      annualPrice: 800,
+      monthlyPriceFactor: 8,
+    });
+
+    for (let i = 1; i < options.length; i++) {
+      expect(options[i].value).toBeGreaterThan(options[i - 1].value);
+    }
+  });
+
+  test('handles custom annualBillingMonths', () => {
+    const options = getBillingOptions({
+      annualBillingMonths: 6,
+      annualPrice: 600,
+      monthlyPriceFactor: 6,
+    });
+
+    // monthlyPrice = 600/6 = 100; months 1-5 stay monthly, month 6 switches to annual
+    const values = options.map((o) => o.value);
+    expect(values).toContain(1);
+    expect(values).toContain(5);
+    // Month 6 switches to annual (6*100 = 600 = annualPrice), so value is 12 (ANNUAL_BILLING_MONTHS)
+    expect(values).not.toContain(6);
+    expect(options.at(-1)?.billingCycle).toBe('year');
+    expect(options.at(-1)?.value).toBe(12);
+  });
+
+  test('every option includes all BillingPlan fields', () => {
+    const options = getBillingOptions({
+      annualPrice: 800,
+      monthlyPriceFactor: 8,
+    });
+
+    for (const opt of options) {
+      expect(typeof opt.requestedMonths).toBe('number');
+      expect(typeof opt.billingMonths).toBe('number');
+      expect(typeof opt.billingCycle).toBe('string');
+      expect(typeof opt.amount).toBe('number');
+      expect(typeof opt.annualPrice).toBe('number');
+      expect(typeof opt.monthlyPrice).toBe('number');
+      expect(typeof opt.monthlyPriceFactor).toBe('number');
+      expect(typeof opt.switchedToAnnual).toBe('boolean');
+      expect(typeof opt.value).toBe('number');
+    }
+  });
 });