[CityOfZion#1318] PrepWork 1/2: Added util/poll.js unit tests

__tests__/util/poll.test.js

@@ -0,0 +1,33 @@
+import poll, { TimeoutError } from '../../app/util/poll'
+
+describe('poll functionality', () => {
+  test('should stop when condition fulflled', async () => {
+    // 10 rounds of 10ms
+    const pollCfg = { attempts: 10, frequency: 10 }
+
+    // pulfill the poll condition after 5th attempt
+    let num = 5
+    const condition = jest.fn(() => {
+      return --num === 0 ? Promise.resolve(num) : Promise.reject()
+    })
+
+    // run poll, expect no exit by error
+    const result = await poll(condition, pollCfg)
+    // expect to have run 5/10 attempts
+    expect(condition).toHaveBeenCalledTimes(5)
+  })
+
+  test('should stop when max attempts reached', async () => {
+    // 10 rounds of 10ms
+    const pollCfg = { attempts: 10, frequency: 10 }
+    // always reject means poll is continuous
+    const condition = jest.fn(() => Promise.reject())
+
+    try {
+      await poll(condition, pollCfg) // run poll
+    } catch (e) {
+      expect(e.name).toBe(TimeoutError.name) // expect it to reach max attempts
+      expect(condition).toHaveBeenCalledTimes(11) // expect to have run 10 (+1) attempts
+    }
+  })
+})

app/util/poll.js

@@ -3,17 +3,24 @@ import delay from './delay'
 const DEFAULT_ATTEMPTS = Infinity
 const DEFAULT_FREQUENCY = 1000
 
+export class TimeoutError extends Error {
+  constructor() {
+    super('Poll reached maximum attempts')
+    this.name = 'TimeoutError'
+  }
+}
+
 export default function poll(
   request,
   { attempts = DEFAULT_ATTEMPTS, frequency = DEFAULT_FREQUENCY } = {}
 ) {
-  return request().catch(function retry(err) {
+  return request().catch(function retry() {
     // eslint-disable-next-line
     if (attempts-- > 0) {
       return delay(frequency)
         .then(request)
         .catch(retry)
     }
-    throw err
+    throw new TimeoutError()
   })
 }