test: add tests for limit-rate util

src/app/utils/__tests__/limit-rate.spec.ts

@@ -0,0 +1,43 @@
+import RateLimit from 'express-rate-limit'
+import expressHandler from 'tests/unit/backend/helpers/jest-express'
+import { mocked } from 'ts-jest/utils'
+
+jest.mock('express-rate-limit')
+const MockRateLimit = mocked(RateLimit, true)
+
+// eslint-disable-next-line import/first
+import { limitRate } from 'src/app/utils/limit-rate'
+
+const MOCK_MAX = 5
+const MOCK_WINDOW = 10
+
+describe('limitRate', () => {
+  beforeEach(() => {
+    jest.clearAllMocks()
+  })
+  it('should create a rate-limiting middleware with defaults', () => {
+    limitRate()
+    expect(MockRateLimit).toHaveBeenCalledWith(
+      expect.objectContaining({ windowMs: 60000, max: 1200 }),
+    )
+  })
+
+  it('should create a rate-limiting middleware with custom options', () => {
+    limitRate({ max: MOCK_MAX, windowMs: MOCK_WINDOW })
+    expect(MockRateLimit).toHaveBeenCalledWith(
+      expect.objectContaining({ windowMs: MOCK_WINDOW, max: MOCK_MAX }),
+    )
+  })
+
+  it('should call next() in the handler', () => {
+    limitRate()
+    const handler = MockRateLimit.mock.calls[0][0]!.handler!
+    const mockNext = jest.fn()
+    handler(
+      expressHandler.mockRequest(),
+      expressHandler.mockResponse(),
+      mockNext,
+    )
+    expect(mockNext).toHaveBeenCalled()
+  })
+})