模拟 AWS 承诺时出现“docClient.scan(...).promise 不是函数”错误

Question

我正在尝试将一些代码从回调更改为承诺，将 .promise 添加到 aws 调用中。

const AWS = require("aws-sdk")

const docClient = new AWS.DynamoDB.DocumentClient({
  apiVersion: "2012-08-10",
  region: process.env.AWS_REGION
})

class Stuff {
   getRawItems() {
     let params = {
        TableName : "TableName"
     }

     return docClient.scan(params).promise()
       .then(function(data) {
          return data.Items
       })
       .catch(function(err) {
         console.warn("Error with Dynamo request", err)
         throw err
       })
   }
}

我认为这是正确的，但测试有问题。我得到了错误：

'TypeError: docClient.scan(...).promise 不是函数'

我认为这与模拟的编写方式有关：

const fakeDynamo = { scan: jest.fn() }

const realAWS = require("aws-sdk")
realAWS.DynamoDB.DocumentClient = jest.fn( () => fakeDynamo )
const Stuff = require("../src/stuff").Stuff

test("Test that the scan is performed and the data comes back", done => {
   fakeDynamo.scan.mockImplementation( () => Promise.resolve({Items:[1,2,3]}))
   const stuff = new Stuff()
   const defaultItems = 
   stuff.getRawItems(lat, lon)
   defaultItems.then ( (data) => {
      expect(fakeDynamo.scan).toHaveBeenCalledTimes(1)
      expect(data.length).toEqual(3)
      done()
 })
})

Answer 1

模拟是问题所在，这里是示例代码：

const fakePromise = {
   promise : jest.fn()
}
const fakeDynamo = { scan: () => {
   return fakePromise
}}

const realAWS = require("aws-sdk")
realAWS.DynamoDB.DocumentClient = jest.fn( () => fakeDynamo )
const Stuff = require("../src/stuff").Stuff

test("Test that the scan is performed and the data comes back", done => {
  fakePromise.promise.mockImplementation(() => Promise.resolve({Items:[1,2,3]}))
  const stuff = new Stuff()
  const defaultItems = stuff.getRawItems(lat, lon)
  defaultItems.then ( (data) => {
     expect(fakePromise.promise).toHaveBeenCalledTimes(1)
     expect(data.length).toEqual(3)
     done()
  })
})

Answer 2

我遇到了这个问题，并找到了最简单的解决方案，即让 mock 发送一个被视为承诺的回调。

fakePromise.promise.mockImplementation((params, callback) => callback(null, {Items:[1,2,3]}))

Answer 3

我想也许可以阅读 Promises

 return docClient.scan(params).promise()
   .then(function(data) {
      return data.Items
   })
   .catch(function(err) {
     console.warn("Error with Dynamo request", err)
     throw err
   })

应该是：

 return docClient.scan(params)
   .then(function(data) {
      return data.Items
   })
   .catch(function(err) {
     console.warn("Error with Dynamo request", err)
     throw err
   })

解析器告诉你：scan 函数的结果中没有 promise 函数。