笑话：函数中的模拟类方法答案

【问题标题】：Jest: Mock class method in a function笑话：函数中的模拟类方法
【发布时间】：2020-05-07 04:13:50
【问题描述】：

所以只是想了解我如何在函数本身中模拟类函数。如何模拟从 exchange.someFunction() 方法返回的数据，以便测试实际的 getPositions() 函数本身？

const library = require('library');
const exchange = new library.exchange_name();

async function getPositions() {

    let positions = [];

    const results = await exchange.someFunction();
    // Do some stuff
    return results;

}

我正在尝试执行以下操作，但不知道我做的是否正确

const exchange = require('../../exchange');
jest.mock('library')

it('get balances', async () => {
    library.someFunction.mockResolvedValue({
        data: [{some data here}]
   )}
}

抛出错误：

TypeError: Cannot read property 'mockResolvedValue' of undefined

【问题讨论】：

标签： javascript unit-testing mocking jestjs

【解决方案1】：

这里是单元测试解决方案：

index.js:

const library = require('./library');
const exchange = new library.exchange_name();

async function getPositions() {
  let positions = [];

  const results = await exchange.someFunction();
  return results;
}

module.exports = getPositions;

library.js:

function exchange_name() {
  async function someFunction() {
    return 'real data';
  }

  return {
    someFunction,
  };
}

module.exports = { exchange_name };

index.test.js:

const getPositions = require('./');
const mockLibrary = require('./library');

jest.mock('./library', () => {
  const mockExchange = { someFunction: jest.fn() };
  return { exchange_name: jest.fn(() => mockExchange) };
});

describe('61649788', () => {
  it('get balances', async () => {
    const mockExchange = new mockLibrary.exchange_name();
    mockExchange.someFunction.mockResolvedValueOnce({ data: ['mocked data'] });
    const actual = await getPositions();
    expect(actual).toEqual({ data: ['mocked data'] });
    expect(mockExchange.someFunction).toBeCalled();
  });
});

100% 覆盖率的单元测试结果：

 PASS  stackoverflow/61649788/index.test.js (8.775s)
  61649788
    ✓ get balances (7ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |                   
 index.js |     100 |      100 |     100 |     100 |                   
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        10.099s

【讨论】：