test(billing): add unit tests for fetchPaymentMethods function

- 6 new tests with Stripe API mocking via mockModule
- Tests combined card+link results, empty results, cards-only, links-only
- Verifies correct API parameters (customer ID, payment method types)
- Verifies cards-first-then-links ordering
- Total: 42 tests for auto-topup-helpers (was 36, now 42)

Author: brandonkachen

packages/billing/src/__tests__/auto-topup-helpers.test.ts

@@ -1,6 +1,11 @@
-import { describe, expect, it } from 'bun:test'
+import {
+  clearMockedModules,
+  mockModule,
+} from '@codebuff/common/testing/mock-modules'
+import { afterEach, beforeEach, describe, expect, it } from 'bun:test'
 
 import {
+  fetchPaymentMethods,
   filterValidPaymentMethods,
   findValidPaymentMethod,
   isValidPaymentMethod,
@@ -54,6 +59,180 @@ function createPaymentMethodWithType(
 }
 
 describe('auto-topup-helpers', () => {
+  describe('fetchPaymentMethods', () => {
+    let mockPaymentMethodsList: ReturnType<typeof createMockPaymentMethodsList>
+
+    function createMockPaymentMethodsList(options?: {
+      cards?: Stripe.PaymentMethod[]
+      links?: Stripe.PaymentMethod[]
+    }) {
+      const cards = options?.cards ?? []
+      const links = options?.links ?? []
+      const calls: Array<{ customer: string; type: string }> = []
+
+      return {
+        calls,
+        list: async (params: { customer: string; type: string }) => {
+          calls.push({ customer: params.customer, type: params.type })
+          if (params.type === 'card') {
+            return { data: cards }
+          }
+          if (params.type === 'link') {
+            return { data: links }
+          }
+          return { data: [] }
+        },
+      }
+    }
+
+    beforeEach(async () => {
+      mockPaymentMethodsList = createMockPaymentMethodsList()
+      await mockModule('@codebuff/internal/util/stripe', () => ({
+        stripeServer: {
+          paymentMethods: mockPaymentMethodsList,
+        },
+      }))
+    })
+
+    afterEach(() => {
+      clearMockedModules()
+    })
+
+    it('should return combined card and link payment methods', async () => {
+      const card1 = createCardPaymentMethod('pm_card_1', 2099, 12)
+      const card2 = createCardPaymentMethod('pm_card_2', 2050, 6)
+      const link1 = createLinkPaymentMethod('pm_link_1')
+
+      mockPaymentMethodsList = createMockPaymentMethodsList({
+        cards: [card1, card2],
+        links: [link1],
+      })
+      await mockModule('@codebuff/internal/util/stripe', () => ({
+        stripeServer: {
+          paymentMethods: mockPaymentMethodsList,
+        },
+      }))
+
+      const result = await fetchPaymentMethods('cus_123')
+
+      expect(result).toHaveLength(3)
+      expect(result[0].id).toBe('pm_card_1')
+      expect(result[1].id).toBe('pm_card_2')
+      expect(result[2].id).toBe('pm_link_1')
+    })
+
+    it('should return empty array when customer has no payment methods', async () => {
+      mockPaymentMethodsList = createMockPaymentMethodsList({
+        cards: [],
+        links: [],
+      })
+      await mockModule('@codebuff/internal/util/stripe', () => ({
+        stripeServer: {
+          paymentMethods: mockPaymentMethodsList,
+        },
+      }))
+
+      const result = await fetchPaymentMethods('cus_456')
+
+      expect(result).toEqual([])
+    })
+
+    it('should return only cards when no link methods exist', async () => {
+      const card1 = createCardPaymentMethod('pm_card_1', 2099, 12)
+      const card2 = createCardPaymentMethod('pm_card_2', 2050, 6)
+
+      mockPaymentMethodsList = createMockPaymentMethodsList({
+        cards: [card1, card2],
+        links: [],
+      })
+      await mockModule('@codebuff/internal/util/stripe', () => ({
+        stripeServer: {
+          paymentMethods: mockPaymentMethodsList,
+        },
+      }))
+
+      const result = await fetchPaymentMethods('cus_789')
+
+      expect(result).toHaveLength(2)
+      expect(result[0].id).toBe('pm_card_1')
+      expect(result[1].id).toBe('pm_card_2')
+    })
+
+    it('should return only links when no card methods exist', async () => {
+      const link1 = createLinkPaymentMethod('pm_link_1')
+      const link2 = createLinkPaymentMethod('pm_link_2')
+
+      mockPaymentMethodsList = createMockPaymentMethodsList({
+        cards: [],
+        links: [link1, link2],
+      })
+      await mockModule('@codebuff/internal/util/stripe', () => ({
+        stripeServer: {
+          paymentMethods: mockPaymentMethodsList,
+        },
+      }))
+
+      const result = await fetchPaymentMethods('cus_abc')
+
+      expect(result).toHaveLength(2)
+      expect(result[0].id).toBe('pm_link_1')
+      expect(result[1].id).toBe('pm_link_2')
+    })
+
+    it('should call Stripe API with correct customer ID and payment method types', async () => {
+      const card = createCardPaymentMethod('pm_card', 2099, 12)
+      const link = createLinkPaymentMethod('pm_link')
+
+      mockPaymentMethodsList = createMockPaymentMethodsList({
+        cards: [card],
+        links: [link],
+      })
+      await mockModule('@codebuff/internal/util/stripe', () => ({
+        stripeServer: {
+          paymentMethods: mockPaymentMethodsList,
+        },
+      }))
+
+      await fetchPaymentMethods('cus_test_customer')
+
+      expect(mockPaymentMethodsList.calls).toHaveLength(2)
+      expect(mockPaymentMethodsList.calls).toContainEqual({
+        customer: 'cus_test_customer',
+        type: 'card',
+      })
+      expect(mockPaymentMethodsList.calls).toContainEqual({
+        customer: 'cus_test_customer',
+        type: 'link',
+      })
+    })
+
+    it('should preserve order with cards first then links', async () => {
+      const card1 = createCardPaymentMethod('pm_card_1', 2099, 12)
+      const link1 = createLinkPaymentMethod('pm_link_1')
+      const card2 = createCardPaymentMethod('pm_card_2', 2050, 6)
+      const link2 = createLinkPaymentMethod('pm_link_2')
+
+      mockPaymentMethodsList = createMockPaymentMethodsList({
+        cards: [card1, card2],
+        links: [link1, link2],
+      })
+      await mockModule('@codebuff/internal/util/stripe', () => ({
+        stripeServer: {
+          paymentMethods: mockPaymentMethodsList,
+        },
+      }))
+
+      const result = await fetchPaymentMethods('cus_order')
+
+      expect(result.map((pm) => pm.id)).toEqual([
+        'pm_card_1',
+        'pm_card_2',
+        'pm_link_1',
+        'pm_link_2',
+      ])
+    })
+  })
+
   describe('isValidPaymentMethod', () => {
     describe('card payment methods', () => {
       it('should return true for card with future expiration date', () => {