Introduction to fs-monkey

fs-monkey is a highly versatile library that allows developers to mock file systems in order to test the behavior of applications. By leveraging this tool, you can simulate file system operations without modifying any real files on the disk. This provides a controlled environment for unit tests and debugging, improving the reliability and performance of your applications.

API Overview

Below are some of the most useful APIs provided by fs-monkey, each illustrated with a code snippet.

1. patchFs()

This function patches the file system so that all fs operations are redirected to the provided mock object.

  const fs = require('fs');
  const memoryFs = require('memfs').fs;
  const { patchFs } = require('fs-monkey');

  patchFs(memoryFs);

  fs.writeFileSync('/example.txt', 'Hello, fs-monkey!');
  const data = fs.readFileSync('/example.txt', 'utf8');
  console.log(data); // Output: Hello, fs-monkey!

2. ufs

The `ufs` API allows you to combine different file system implementations.

  const { ufs } = require('unionfs');
  const memfs = require('memfs');
  const realFs = require('fs');

  ufs
    .use(memfs)
    .use(realFs);

  fs.writeFileSync('/virtual.txt', 'This is a virtual file.');
  const virtualData = fs.readFileSync('/virtual.txt', 'utf8');
  console.log(virtualData); // Output: This is a virtual file.

3. unpatchFs()

Unpatch the file system to return to the original fs behavior.

  const { unpatchFs } = require('fs-monkey');

  unpatchFs();

  fs.writeFileSync('original.txt', 'Back to original FS.');
  const originalData = fs.readFileSync('original.txt', 'utf8');
  console.log(originalData); // Output: Back to original FS.

Sample Application Using fs-monkey

Here’s a small application that demonstrates the combined use of these APIs to create a mock file system for testing purposes.

  const fs = require('fs');
  const { ufs } = require('unionfs');
  const memfs = require('memfs');
  const { patchFs, unpatchFs } = require('fs-monkey');

  // Step 1: Patch the file system using memory filesystem
  patchFs(memfs.fs);

  // Step 2: Perform some mock file operations
  fs.writeFileSync('/test-file.txt', 'This is a test file.');
  let content = fs.readFileSync('/test-file.txt', 'utf8');
  console.log('Mock FS:', content); // Output: This is a test file.

  // Step 3: Unpatch to revert back to real file system
  unpatchFs();

  // Step 4: Perform real file operations
  fs.writeFileSync('real-file.txt', 'This is a real file.');
  content = fs.readFileSync('real-file.txt', 'utf8');
  console.log('Real FS:', content); // Output: This is a real file.

Conclusion

fs-monkey is a powerful tool that provides a straightforward way to mock and test file system operations. By understanding and leveraging its APIs, you can enhance the reliability and maintainability of your applications.

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