node-builtins-mocks

Generates mocks for all node-builtins. Builtins are modules such as fs, url, path, and http.

Why?

Because I'm lazy, and writing this:

const generateMocks = require('node-builtins-mocks');
const sinon = require('sinon');
const mocks = generateMocks(sinon.stub);

is faster than writing this:

const sinon = require('sinon');
const mocks = {
  fs: {
    readdir: sinon.stub(),
    createReadStream: sinon.stub()
  },
  os: {
    platform: sinon.stub()
  },
  crypto: {
    createHash: sinon.stub()
  }
};

Install

# install and persist to "devDependencies" in package.json

npm i node-builtins-mocks -D

Usage

basic usage example

Below we use sinon.stub, but you can pass any function to be used as a stub generator:

// we will use the stub method from sinon as a stub generator for mocks
const sinon = require('sinon');

// this function will allow us to generate all the mocks we need...
const generateMocks = require('node-builtins-mocks')

// .. and now we have some mocks that we can configure
const mocks = generateMocks(sinon.stub);

// make the "fs.readdir" mock return data
mocks.fs.readdir.yields(null, ['index.html', 'favicon.ico']);

// or make dns lookups fail
mocks.dns.resolve.yields(new Error('EADDRNOTAVAIL'));

advanced usage example

Bear in mind, this is just an example of usage, if you don't like proxyquire, mocha, or sinon for testing you can use different mocking modules or techniques.

proxyquire is a neat module for stubbing dependencies during testing. Here's an example of how we can mock out the fs module using node-builtins-mocks and proxyquire.

Here's our module:

const fs = require('fs'); // we're going to stub this out for tests
const path = require('path');

// read all files in a directory and return those with a given extension
module.exports = function (dir, extension) {
  return fs.readdirSync(dir).filter((filename) => {
    return path.extname(filename) === extension;
  });
};

And a test for it:

const proxyquire = require('proxyquire');
const sinon = require('sinon');
const mocks = require('node-builtins-mocks')(sinon.stub);
const assert = require('assert');

var getFiles = proxyquire('./get-files-in-directory-with-extension.js', {
  // proxyquire will inject this fs stub instead of the real fs module when
  // get-files-in-directory-with-extension.js calls "require('fs')"
  fs: mocks.fs
});

describe('get-files', function () {
  it('should return 2 .js files', function () {
    // make our stub return a fake file list
    mocks.fs.readdirSync.returns(['a.html', 'b.js', 'c.js']);

    // call function that relies on our fs.readdirSync stub
    const files = getFiles('./', '.js');

    // only .js files should have been returned as per our stub
    assert.equal(files.length, 2);
    assert.deepEqual(files, ['b.js', 'c.js']);
  });
});