javascript - 在 Jest 中模拟 Lambda 回调？ (无法读取未定义的属性体)

Question

我正在尝试对 lambda 函数进行单元测试，但不知道如何模拟 lambda callback所以它停止代码执行。 callback我模拟被调用，在 lambda 的情况下会立即返回响应。但是，在我的单元测试中，它继续执行代码，但出现错误:

TypeError: Cannot read property 'body' of undefined

我对 Jest 比较陌生，所以不知道如何继续。 example.js ( lambda 代码)

// dependencies
const got = require('got');

// lambda handler
const example = async (event, context, callback) => {
  // message placeholder
  let message;

  // set request options
  const gotOptions = {
    json: {
      process: event.process
    },
    responseType: 'json'
  };

  // http response data
  const res = await got.post('https://some.url/api/process', gotOptions).catch((error) => {
    message = 'error calling process';

    // log and return the error
    console.log(message, error);
    callback(message);
  });

  // res.body is causing the error in the test since
  // this code still executes after callbacks triggered
  message = `Process ${event.process} is: ${res.body.active}`;


  callback(null, message);
};


// export example
exports.example = example;

example.test.js (单元测试代码)

// get the lib we want to test
const example = require('./example');

// setup mocks
jest.mock('got');

// mock our lambda callback
const callback = jest.fn();


// import the modules we want to mock
const got = require('got');


// set default event
let event = {
  process: 1
};

// set default context
const context = {};


// run before each test
beforeEach(() => {
  // set default got.post response
  got.post.mockReturnValue(Promise.resolve({
    body: {
      active: true
    }
  }));
});

// test artifact api
describe('[example]', () => {
  ...other tests that pass...

  test('error calling process api', async () => {
    let error = 'error calling process';

    // set got mock response for this test to error
    got.post.mockReturnValue(Promise.reject(error));

    // function we want to test w/ mock data
    await example.example(event, context, callback);

    // test our callback function to see if it matches our desired expectedResponse
    expect(callback).toHaveBeenCalledWith(error);
  });
});

Answer 1

您需要模拟 callback 的实现功能。为了在错误处理后停止执行代码，您需要throw new Error() ，并使用 await expect(example.example(event, context, callback)).rejects.toThrow(error);捕获错误以避免测试失败。这样我们就可以模拟 aws lambda 的行为了
例如。example.js :

const got = require('got');

const example = async (event, context, callback) => {
  let message;

  const gotOptions = {
    json: {
      process: event.process,
    },
    responseType: 'json',
  };

  const res = await got.post('https://some.url/api/process', gotOptions).catch((error) => {
    callback(error);
  });

  console.log('process');
  message = `Process ${event.process} is: ${res.body.active}`;

  callback(null, message);
};

exports.example = example;

example.test.js :

const example = require('./example');
const got = require('got');

jest.mock('got');
const callback = jest.fn().mockImplementation((errorMsg) => {
  if (errorMsg) throw new Error(errorMsg);
});
const event = { process: 1 };
const context = {};

describe('[example]', () => {
  test('error calling process api', async () => {
    let error = 'error calling process';
    got.post.mockRejectedValueOnce(error);
    await expect(example.example(event, context, callback)).rejects.toThrow(error);
    expect(callback).toHaveBeenCalledWith(error);
  });

  test('should success', async () => {
    got.post.mockResolvedValueOnce({
      body: { active: true },
    });
    await example.example(event, context, callback);
    expect(callback).toHaveBeenCalledWith(null, 'Process 1 is: true');
  });
});

测试结果:

 PASS  examples/66567679/example.test.js
  [example]
    ✓ error calling process api (5 ms)
    ✓ should success (10 ms)

  console.log
    process

      at examples/66567679/example.js:17:11

------------|---------|----------|---------|---------|-------------------
File        | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
------------|---------|----------|---------|---------|-------------------
All files   |     100 |      100 |     100 |     100 |                   
 example.js |     100 |      100 |     100 |     100 |                   
------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        3.966 s, estimated 4 s