init

.eslintignore

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+dist/
+old-code/
+dev/
+node_modules

.eslintrc.js

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+module.exports = {
+  env: {
+    es6: true,
+    node: true,
+    jest: true
+  },
+  extends: ['google', 'prettier'],
+  plugins: ['prettier'],
+  globals: {
+    Atomics: 'readonly',
+    SharedArrayBuffer: 'readonly'
+  },
+  parserOptions: {
+    ecmaVersion: 2018
+  },
+  rules: {
+    'prettier/prettier': ['error'],
+    'comma-dangle': 0,
+    'require-jsdoc': 0,
+    'arrow-parens': 0,
+    'guard-for-in': 0,
+    'valid-jsdoc': 0,
+    'no-undef': 'error',
+    'operator-linebreak': [
+      'error',
+      'after',
+      {
+        overrides: { '?': 'ignore', ':': 'ignore', '+': 'ignore' }
+      }
+    ],
+    indent: [
+      'error',
+      2,
+      {
+        CallExpression: { arguments: 'first' },
+        ignoredNodes: [
+          'CallExpression > CallExpression',
+          'CallExpression > MemberExpression'
+        ],
+        SwitchCase: 1
+      }
+    ],
+    'max-len': ['error', { code: 80, ignoreComments: true }]
+  }
+};

.gitignore

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+node_modules

.npmignore

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+node_modules
+.vscode
+examples
+.eslintignore
+.eslintrc.js
+.prettierignore
+.prettierrc

.prettierignore

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+dist/
+old-code/
+dev/

.prettierrc

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+{
+  "semi": true,
+  "singleQuote": true,
+  "printWidth": 80,
+  "trailingComma": "none"
+}

.vscode/settings.json

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+{
+  "editor.formatOnSave": true
+}

README.md

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+# jest-mock-fs
+
+Node's `fs` mock for [jest](https://jestjs.io/).
+
+## APIs Implemented
+- [x] `fs.readFileSync`
+- [x] `fs.readdirSync`
+- [x] `fs.writeFileSync`
+- [x] `fs.readFile`
+- [x] `fs.readdir`
+- [x] `fs.writeFile`
+- [ ] `fs.stat`
+- [ ] `fs.unlink`
+- [ ] `fs.mkdir`
+- [ ] `fs.rmdir`
+
+## Setup
+
+**Step 1:** Install library
+```sh
+npm i --save-dev jest-mock-fs
+```
+
+**Step 2:** Create a mock and re-export library
+Inside your `tests/__mocks__/fs.js`
+```js
+const fs = require('jest-mock-fs');
+module.exports = fs;
+```
+
+**Step 3:** Add mock
+Inside your `tests/example.test.js`
+```js
+jest.mock('fs');
+```
+
+<details>
+<summary>View Full <code>example.test.js</code> file</summary>
+
+```js
+const fs = require('fs');
+jest.mock('fs');
+
+test('should return content', async () => {
+  // This will not create an actual file in your file system
+  fs.writeFileSync('test.txt', 'test');
+  const content = fs.readFileSync('test.txt', 'utf-8');
+  expect(content).toBe('test');
+});
+
+```
+</details>

examples/__mocks__/fs.js

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+const fs = require('../../lib');
+module.exports = fs;

examples/test1.test.js

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+const fs = require('fs');
+jest.mock('fs');
+const { getMockFs } = require('../lib/helpers');
+
+test('should pass', async () => {
+  fs.writeFileSync('test.txt', 'test');
+  const content = fs.readFileSync('test.txt');
+  console.log(getMockFs());
+  expect(content).toBe('test');
+});

lib/helpers.js

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+const fs = require('fs');
+
+module.exports = {
+  getMockFs: fs.__getMockFs
+};

lib/index.js

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+const fs = jest.createMockFromModule('fs');
+
+const mockFs = {};
+
+fs.readFile = async (...args) => fs.readFileSync(...args);
+
+fs.writeFile = async (...args) => {
+  fs.writeFileSync(...args);
+  return Promise.resolve();
+};
+
+fs.readFileSync = (filePath, encoding) => {
+  const content = mockFs[filePath];
+  if (typeof encoding === 'string' && encoding.includes('utf')) {
+    return content;
+  }
+
+  return Buffer.from(content, 'utf8');
+};
+
+fs.writeFileSync = (filePath, content) => {
+  mockFs[filePath] = content;
+};
+
+fs.existsSync = (filePath) => !!mockFs[filePath];
+
+fs.readdirSync = (dirPath) => {
+  const files = Object.keys(mockFs).filter((filePath) =>
+    filePath.startsWith(dirPath)
+  );
+  return files;
+};
+
+fs.__getMockFs = () => mockFs;
+
+module.exports = fs;