Jest -嘲弄FS模块和调用config模块时得到错误

Question

我正在用Jest编写单元测试，试图测试一个使用FS的模块。

模块文件:

import fs from 'fs';
import logger from './logger.utils';
export const getNumberOfFiles = async (targetDir: string): Promise<number> => {
// get number of folders
logger.info(`getNumberOfFiles from ${targetDir}/${fileName}`);
const numberOfFiles = await fs.readdirSync(targetDir);
return numberOfFiles.length;
};

测试文件

import fs from 'fs';
import { getNumberOfFiles } from '../../src/utils/fs.utils';
jest.mock('fs');
describe('fs.utils', () => {
describe('getNumberOfFiles', () => {
it('Should return number', async () => {
fs.readdirSync = jest.fn();
const readdirSyncMock = fs.readdirSync = jest.fn();
readdirSyncMock.mockResolvedValue([1, 2, 3]);
const result = await getNumberOfFiles('targetDir');
expect(result).toEqual(3);
expect(readdirSyncMock.mock.calls.length).toEqual(1);
});
});
});

当我运行测试文件时，我得到以下错误:

配置文件..../Config/runtime。无法读取Json。错误码为:undefined。错误信息是:无法读取未定义

的属性'replace'

1 | const cheggLogger = require('@chegg/logger');
2 | import loggingContext from './loggingContext';
> 3 | import config from 'config';
| ^
4 | import os from 'os';
5 | import constants from '../../config/constants';
6 | 
at Config.Object.<anonymous>.util.parseFile (node_modules/config/lib/config.js:789:13)
at Config.Object.<anonymous>.util.loadFileConfigs (node_modules/config/lib/config.js:666:26)
at new Config (node_modules/config/lib/config.js:116:27)
at Object.<anonymous> (node_modules/config/lib/config.js:1459:31)
at Object.<anonymous> (src/utils/logger.utils.ts:3:1)

logger.utils.ts的内容

const internalLogger = require('internalLogger');
import loggingContext from './loggingContext';
import config from 'config';
import os from 'os';
import constants from '../../config/constants';
const logger = internalLogger.createLogger({
level: config.get(constants.LOG_LEVEL)
});
export default logger;

我假设config正在使用FS，一旦我模拟模块，它就失败了。我该如何解决这个问题?请通知

Answer 1

我猜问题来自config也使用fsapi，但你现在模拟整个模块fs，这使得所有方法在使用之前都应该被模拟。

但是我有一个想法，通过使用jest.doMock，你可以为每个测试提供一个工厂，只是模拟我们需要的唯一方法。这是一个草稿:

describe('fs.utils', () => {
describe('getNumberOfFiles', () => {
it('Should return number', async () => {
jest.doMock('fs', () => ({
// Keep other methods still working so `config` or others can use
// so make sure we don't break anything
...jest.requireActual('fs'),
readdirSync: jest.fn(pathUrl => {
// Mock for our test path since `config` also uses this method :(
return pathUrl === 'targetDir' ? Promise.resolve([1, 2, 3]) : jest.requireActual('fs').readdirSync(pathUrl)
})
}));

// One of the thing we should change is to switch `require` here
// to make sure the mock is happened before we actually require the code
// we can also use `import` here but requires us do a bit more thing
// so I keep thing simple by using `require`
const {getNumberOfFiles} = require('../../src/utils/fs.utils');

const result = await getNumberOfFiles('targetDir');
expect(result).toEqual(3);
// you might stop assert this as well
// expect(readdirSyncMock.mock.calls.length).toEqual(1);
});
});
});

还想检查一下，如果您创建了如下所述的配置文件:https://www.npmjs.com/package/config#quick-start