如何用Jest伪装`fs.promises.writeFile`
如何用Jest伪装`fs.promises.writeFile`
提问于 2020-11-21 20:32:39
我试图使用Jest来模拟promise版本的fs.writeFile，并且没有调用被模拟的函数。
要测试的函数(createFile.js)
const { writeFile } = require("fs").promises;
const createNewFile = async () => {
await writeFile(`${__dirname}/newFile.txt`, "Test content");
};
module.exports = {
createNewFile,
};Jest测试(createFile.test.js)：
const fs = require("fs").promises;
const { createNewFile } = require("./createFile.js");
it("Calls writeFile", async () => {
const writeFileSpy = jest.spyOn(fs, "writeFile");
await createNewFile();
expect(writeFileSpy).toHaveBeenCalledTimes(1);
writeFileSpy.mockClear();
});我知道writeFile实际上是被调用的，因为我运行了node -e "require(\"./createFile.js\").createNewFile()"并创建了该文件。
依赖关系版本
- Node.js: 14.1.0
- Jest: 26.6.3
-这是对createFile.test.js文件的另一次尝试--
const fs = require("fs");
const { createNewFile } = require("./createFile.js");
it("Calls writeFile", async () => {
const writeFileMock = jest.fn();
jest.mock("fs", () => ({
promises: {
writeFile: writeFileMock,
},
}));
await createNewFile();
expect(writeFileMock).toHaveBeenCalledTimes(1);
});这会引发以下错误：
ReferenceError: /Users/danlevy/Desktop/test/src/createFile.test.js: The module factory of `jest.mock()` is not allowed to reference any out-of-scope variables.
Invalid variable access: writeFileMock回答 3
Stack Overflow用户
回答已采纳
发布于 2020-11-21 21:09:55
由于writeFile是在导入时被解构的，而不是一直被称为fs.promises.writeFile方法，所以它不会受到spyOn的影响。
它应该被模仿为任何其他模块：
jest.mock("fs", () => ({
promises: {
writeFile: jest.fn().mockResolvedValue(),
readFile: jest.fn().mockResolvedValue(),
},
}));
const fs = require("fs");
...
await createNewFile();
expect(fs.promises.writeFile).toHaveBeenCalledTimes(1);模拟fs是很有意义的，因为非模拟的函数提供了副作用，并可能对测试环境产生负面影响。
Stack Overflow用户
发布于 2022-01-30 01:58:51
在jest中模拟“fs/答应”异步函数
下面是一个使用fs.readdir()的简单示例，但它也适用于任何其他异步fs/允诺函数。
files.service.test.js
import fs from "fs/promises";
import FileService from "./files.service";
jest.mock("fs/promises");
describe("FileService", () => {
var fileService: FileService;
beforeEach(() => {
// Create a brand new FileService before running each test
fileService = new FileService();
// Reset mocks
jest.resetAllMocks();
});
describe("getJsonFiles", () => {
it("throws an error if reading the directory fails", async () => {
// Mock the rejection error
fs.readdir = jest.fn().mockRejectedValueOnce(new Error("mock error"));
// Call the function to get the promise
const promise = fileService.getJsonFiles({ folderPath: "mockPath", logActions: false });
expect(fs.readdir).toHaveBeenCalled();
await expect(promise).rejects.toEqual(new Error("mock error"));
});
it("returns an array of the .json file name strings in the test directory (and not any other files)", async () => {
const allPotentialFiles = ["non-json.txt", "test-json-1.json", "test-json-2.json"];
const onlyJsonFiles = ["test-json-1.json", "test-json-2.json"];
// Mock readdir to return all potential files from the dir
fs.readdir = jest.fn().mockResolvedValueOnce(allPotentialFiles);
// Get the promise
const promise = fileService.getJsonFiles({ folderPath: "mockPath", logActions: false });
expect(fs.readdir).toBeCalled();
await expect(promise).resolves.toEqual(onlyJsonFiles); // function should only return the json files
});
});
});files.service.ts
import fs from "fs/promises";
export default class FileService {
constructor() {}
async getJsonFiles(args: FilesListArgs): Promise<string[]> {
const { folderPath, logActions } = args;
try {
// Get list of all files
const files = await fs.readdir(folderPath);
// Filter to only include JSON files
const jsonFiles = files.filter((file) => {
return file.includes(".json");
});
return jsonFiles;
} catch (e) {
throw e;
}
}
}Stack Overflow用户
发布于 2021-07-17 15:52:55
我知道这是一个旧线程，但在我的例子中，我想处理与readFile (或者在您的例子中是writeFile )不同的结果。因此，我使用了Estus建议的解决方案，区别在于我在每个测试中处理readFile的每个实现，而不是使用mockResolvedValue。
我也在用打字本。
import { getFile } from './configFiles';
import fs from 'fs';
jest.mock('fs', () => {
return {
promises: {
readFile: jest.fn()
}
};
});
describe('getFile', () => {
beforeEach(() => {
jest.resetAllMocks();
});
it('should return results from file', async () => {
const mockReadFile = (fs.promises.readFile as jest.Mock).mockImplementation(async () =>
Promise.resolve(JSON.stringify('some-json-value'))
);
const res = await getFile('some-path');
expect(mockReadFile).toHaveBeenCalledWith('some-path', { encoding: 'utf-8' });
expect(res).toMatchObject('some-json-value');
});
it('should gracefully handle error', async () => {
const mockReadFile = (fs.promises.readFile as jest.Mock).mockImplementation(async () =>
Promise.reject(new Error('not found'))
);
const res = await getFile('some-path');
expect(mockReadFile).toHaveBeenCalledWith('some-path', { encoding: 'utf-8' });
expect(res).toMatchObject('whatever-your-fallback-is');
});
});请注意，为了使fs.promises.readFile适用于TS，我必须将它转换为jest.Mock。
而且，我的configFiles.ts看起来像这样：
import { promises as fsPromises } from 'fs';
const readConfigFile = async (filePath: string) => {
const res = await fsPromises.readFile(filePath, { encoding: 'utf-8' });
return JSON.parse(res);
};
export const getFile = async (path: string): Promise<MyType[]> => {
try {
const fileName = 'some_config.json';
return readConfigFile(`${path}/${fileName}`);
} catch (e) {
// some fallback value
return [{}];
}
};页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/64947786
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