mock fs.readFile with typescript

huangapple
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英文:

mock fs.readFile with typescript

问题

I'm here to help with your code translation. Here's the translated code:

  1. 我试图模拟 fs.readFile：
  2. ```javascript
  3. fs.readFile = jest.fn((_, callback) => callback(null, JSON.stringify('sample')));

我试图测试这个函数：

  1. export const readFileAsynchronously = async (pathToFile: string) => {
  2.   const fullPath = join(__dirname, pathToFile);
  3.   if (existsSync(fullPath)) {
  4.     const fileContent = await readFile(fullPath);
  5.     return fileContent.toString();
  6.   }
  8.   return null;
  9. };

我想测试这个函数而不读取实际文件，是否可能？
测试如下：

  1. test('如果文件存在应返回文件内容', async () => {
  2.     jest.mock('fs');
  3.     const existsSync = () => true;
  4.     fs.existsSync = existsSync;
  5.     fs.readFile = jest.fn((_, callback) => {
  6.       return callback(null, JSON.stringify('sample'));
  7.     });
  8.     jest.mock('path');
  9.     path.join = (path: string) => path;
  10.     const pathToFile = './test.txt';
  11.     const result = await readFileAsynchronously(pathToFile);
  12.     expect(result).toEqual('sample');
  13.   });

但我遇到了一个类型错误：
类型“Mock<any, [_: any, callback: any], any>”中未提供属性“promisify”，而在类型“typeof readFile”中是必需的。

我尝试了另一种变体：

  1. const mockedFs = fs as jest.Mocked<typeof fs>;
  2. const existsSync = () => true;
  3. fs.existsSync = existsSync;
  4. mockedFs.readFile.mockImplementationOnce(
  5.   () =>
  6.     new Promise(function (resolve) {
  7.       return resolve('test');
  8.     }),
  9. );

但我收到了一个错误：
TypeError: mockedFs.readFile.mockImplementationOnce 不是一个函数

我不知道如何解决它。请问能否帮助我？

  2. I hope this helps with your code translation. If you have any further questions or need assistance with specific issues in the code, please feel free to ask.
  4. <details>
  5. <summary>英文:</summary>
  7. I&#39;m trying to mock fs.readFile:

fs.readFile = jest.fn((_, callback) => callback(null, JSON.stringify('sample')));

  1. I&#39; m trying to test this function:

export const readFileAsynchronously = async (pathToFile: string) => {
const fullPath = join(__dirname, pathToFile);
if (existsSync(fullPath)) {
const fileContent = await readFile(fullPath);
return fileContent.toString();
}

return null;
};

  1. And I want to test this function without reading the real file, is it possible? 
  2. The test is:

test('should return file content if file exists', async () => {
jest.mock('fs');
const existsSync = () => true;
fs.existsSync = existsSync;
fs.readFile = jest.fn((_, callback) => {
return callback(null, JSON.stringify('sample'));
});
jest.mock('path');
path.join = (path: string) => path;
const pathToFile = './test.txt';
const result = await readFileAsynchronously(pathToFile);
expect(result).toEqual('sample');
});

  1. But I&#39;ve got a type error 
  2. Property `__promisify__` is not presented in type &quot;Mock&lt;any, [_: any, callback: any], any&gt;&quot; and is required in type &quot;typeof readFile&quot;.
  3. I&#39;ve tried one more variant:

const mockedFs = fs as jest.Mocked<typeof fs>;
const existsSync = () => true;
fs.existsSync = existsSync;
mockedFs.readFile.mockImplementationOnce(
() =>
new Promise(function (resolve) {
return resolve('test');
}),
);

  1. But I&#39;ve got an error:

TypeError: mockedFs.readFile.mockImplementationOnce is not a function

  2. I don&#39;t have any idea how to solve it. Please, could you help me? 
  4. </details>
  7. # 答案1
  8. **得分**: 1
  10. 首先，`readFile` 不是一个 promise。你需要使用一个回调或者使用一个不同的函数 `readFileSync`。
  12. 你的函数实现不正确，下面是修复后的版本：
  14. ```typescript
  15. import { join } from 'path';
  16. import { existsSync, readFile } from 'fs';
  17. export const readFileAsynchronously = async (pathToFile: string) => {
  18.   const fullPath = join(__dirname, pathToFile);
  19.   if (existsSync(fullPath)) {
  20.     // 当回调被调用时，使其解析
  21.     return new Promise((resolve, reject) => {
  22.       readFile(fullPath, 'utf8', (error, fileContent) => {
  23.         if (error) return reject(error);
  24.         resolve(fileContent);
  25.       });
  26.     });
  27.   }
  29.   return Promise.reject(new Error('文件未找到'));
  30. };

以下是你的测试实现：

  1. jest.mock('fs', () => ({
  2.   existsSync: jest.fn().mockResolvedValue(true),
  3.   readFile: jest.fn().mockImplementation((path, options, callback) => {
  4.     callback(null, '我的文件内容');
  5.   }),
  6. }));
  8. test('应该在不实际读取文件的情况下解析', async () => {
  9.   const result = await readFileAsynchronously('test.txt');
  10.   expect(result).toBe('我的文件内容');
  11. });
英文:

First of all readFile is not a promise. You need to use a callback or use a different function readFileSync.

Your function is not implemented correctly, here is the fixed version

  1. import { join } from &#39;path&#39;;
  2. import { existsSync, readFile } from &#39;fs&#39;;
  3. export const readFileAsynchronously = async (pathToFile: string) =&gt; {
  4.   const fullPath = join(__dirname, pathToFile);
  5.   if (existsSync(fullPath)) {
  6.     // Making it to resolve when callback is invoked
  7.     return new Promise((resolve, reject) =&gt; {
  8.       readFile(fullPath, &#39;utf8&#39;, (error, fileContent) =&gt; {
  9.         if (error) return reject(error);
  10.         resolve(fileContent);
  11.       });
  12.     });
  13.   }
  15.   return Promise.reject(new Error(&#39;File not found&#39;));
  16. };

And here is your test implementation

  1. jest.mock(&#39;fs&#39;, () =&gt; ({
  2.   existsSync: jest.fn().mockResolvedValue(true),
  3.   readFile: jest.fn().mockImplementation((path, options, callback) =&gt; {
  4.     callback(null, &#39;my file content&#39;);
  5.   }),
  6. }));
  8. test(&#39;should resolve without reading the actual file&#39;, async () =&gt; {
  9.   const result = await readFileAsynchronously(&#39;test.txt&#39;);
  10.   expect(result).toBe(&#39;my file content&#39;);
  11. });

huangapple
  • 本文由 发表于 2023年6月30日 00:39:32
  • 转载请务必保留本文链接：https://go.coder-hub.com/76583018.html
  • jestjs
  • mocking
  • typescript
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