node.js - 使用 Jest 和 mock-fs 测试 async fs.readfile 会导致测试超时,即使超时 30 秒
问题描述
我有一个函数可以使用 Node 的 fs 从文件系统中异步读取文件的内容。虽然该功能有效,但我无法使用 Jest 对其进行测试。我正在使用 mock-fs 库来模拟文件系统以尝试测试该功能。
读取文件的函数:read-file-contents.ts
import * as NodeJSFS from 'fs';
import * as NodeJSPath from 'path';
export async function ReadFileContents(Directory:string, FileName:string):Promise<string> {
return new Promise<string>((resolve, reject) => {
const PathAndFileName = NodeJSPath.format( { dir: Directory, base: FileName });
NodeJSFS.readFile(
PathAndFileName,
(error: NodeJS.ErrnoException | null, FileContents: Buffer) => {
if (error) {
reject(error);
} else {
resolve(FileContents.toString());
}
},
);
});
}
由于mock-fs中有一个目录和一个文件,测试文件确实使mock-fs正常工作,因为文件计数正确返回。错误处理例程工作并捕获文件未找到处理,然后通过。
但是,从模拟中读取实际文件的测试失败。读取文件内容.spec.ts
import * as MockFS from 'mock-fs';
import { ReadFileContents } from './read-file-contents';
describe('ReadFileContents', () => {
afterEach( () => {
MockFS.restore();
});
beforeEach( () => {
MockFS( {
'datafiles': {
'abc.txt': 'Server Name'
}
}, {
// add this option otherwise node-glob returns an empty string!
createCwd: false
} );
});
it('should have the proper number of directories and files in the mocked data', () => {
expect(MockFS.length).toBe(2);
});
it('should error out when file does not exist', async () => {
try {
await ReadFileContents('./', 'file-does-not.exist');
} catch (Exception) {
expect(Exception.code).toBe('ENOENT');
}
});
it('should load the proper data from abc.txt', async () => {
let FileContents:string;
try {
FileContents = await ReadFileContents('./datafiles', 'abc.txt');
expect(FileContents).toBe('Server Name');
} catch (Exception) {
console.log(Exception);
expect(true).toBeFalsy(); // Should not happen due to mock-fs file system
}
});
});
最后一次测试在 30 秒内未返回,并出现以下错误:
FAIL src/library/file-handling/read-file-contents.spec.ts (57.175 s)
● ReadFileContents › should load the proper file data abc.hdr
thrown: "Exceeded timeout of 30000 ms for a test.
Use jest.setTimeout(newTimeout) to increase the timeout value, if this is a long-running test."
22 | });
23 |
> 24 | it('should load the proper file data abc.hdr', async () => {
| ^
25 | let FileContents:string;
26 | try {
27 | FileContents = await ReadFileContents('./datafiles', 'abc.hdr' );
解决方案
In looking for more help, I found the solution. I am using Node 15.9 currently, and since Node 10 (or 12 anyhow), the promises library handles the fs functions much better.
Therefore, my ReadFileContents() code has become much simpler, as I can simply use the promise version of FS readFile from fs/promises. This way the error will be thrown, or the file will be read asynchronously, and the code using this function, which already has a try/catch, will handle the data or catching the thrown error.
import * as NodeJSFSPromises from 'fs/promises';
import * as NodeJSPath from 'path';
export async function ReadFileContents(Directory:string, FileName:string):Promise<string> {
const PathAndFileName = NodeJSPath.format( { dir: Directory, base: FileName });
const FileContents$:Promise<Buffer> = NodeJSFSPromises.readFile(PathAndFileName);
const Contents:string = (await FileContents$).toString();
return Contents;
}
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