proxyquire

What is proxyquire?

Proxyquire is a powerful tool for stubbing and mocking dependencies in Node.js unit tests. It allows you to override dependencies during testing without modifying the actual code, making it easier to isolate and test individual modules.

What are proxyquire's main functionalities?

Basic Dependency Override

This feature allows you to override a dependency with a mock implementation. In this example, the './dependency' module's 'myFunction' is replaced with a mock function that returns 'mocked value'.

const proxyquire = require('proxyquire');
const myModule = proxyquire('./myModule', {
  './dependency': { myFunction: () => 'mocked value' }
});
console.log(myModule.useDependency()); // Outputs: 'mocked value'

Override Multiple Dependencies

This feature allows you to override multiple dependencies at once. In this example, both './dependency1' and './dependency2' are replaced with mock implementations.

const proxyquire = require('proxyquire');
const myModule = proxyquire('./myModule', {
  './dependency1': { myFunction1: () => 'mocked value 1' },
  './dependency2': { myFunction2: () => 'mocked value 2' }
});
console.log(myModule.useDependencies()); // Outputs: 'mocked value 1 and mocked value 2'

Conditional Overrides

This feature allows you to conditionally override dependencies based on certain conditions, such as environment variables. In this example, the './dependency' module is only mocked if the TEST_ENV environment variable is set.

const proxyquire = require('proxyquire');
const myModule = proxyquire('./myModule', {
  './dependency': process.env.TEST_ENV ? { myFunction: () => 'mocked value' } : require('./dependency')
});
console.log(myModule.useDependency()); // Outputs: 'mocked value' if TEST_ENV is set, otherwise the real value

Other packages similar to proxyquire

sinon

Sinon is a popular library for creating spies, stubs, and mocks in JavaScript. Unlike Proxyquire, which focuses on overriding dependencies, Sinon provides a more comprehensive set of tools for creating test doubles and verifying interactions.

rewire

Rewire is another library that allows you to modify the behavior of modules during testing. It provides a similar functionality to Proxyquire but with a different API. Rewire allows you to access private variables and functions within a module, which can be useful for more fine-grained control.

mock-require

Mock-require is a simpler alternative to Proxyquire that allows you to mock Node.js modules. It provides a straightforward API for replacing modules with mock implementations, but it lacks some of the advanced features of Proxyquire.

README

proxyquire

Proxies nodejs's require in order to make overriding dependencies during testing easy while staying totally unobstrusive.

Features

• no changes to your code are necessary
• non overriden methods of a module behave like the original
• "use strict" compliant

Example

foo.js:

var path = require('path');

module.exports.extnameAllCaps = function (file) { 
  return path.extname(file).toUpperCase();
};

module.exports.basenameAllCaps = function (file) { 
  return path.basename(file).toUpperCase();
};

foo.test.js:

var proxyquire =  require('proxyquire')
  , assert     =  require('assert')
  , pathStub   =  { };

// when no overrides are specified, path.extname behaves normally
var foo = proxyquire.resolve('./foo', __dirname, { 'path': pathStub });
assert.equal(foo.extnameAllCaps('file.txt'), '.TXT');

// override path.extname
pathStub.extname = function (file) { return 'Exterminate, exterminate the ' + file; };

// path.extname now behaves as we told it to
assert.equal(foo.extnameAllCaps('file.txt'), 'EXTERMINATE, EXTERMINATE THE FILE.TXT');

// path.basename and all other path module methods still function as before
assert.equal(foo.basenameAllCaps('/a/b/file.txt'), 'FILE.TXT');

Table of Contents generated with DocToc

• Usage
• API
  • Resolve module to be tested and configure stubs
  • Preventing call thru to original dependency
  • Changing the TmpDir
  • Examples
• More Examples

Usage

Two simple steps to override require in your tests:

• add var proxyquire = require('proxyquire'); to top level of your test file
• proxyquire.resolve(...) the module you want to test and pass along stubs for modules you want to override

API

Resolve module to be tested and configure stubs

proxyquire.resolve({string} mdl, {string} test__dirname, {Object} stubs)

• mdl: path to the module to be tested e.g., ../lib/foo
• test__dirname: the __dirname of the module containing the tests
• stubs: key/value pairs of the form { modulePath: stub, ... }
  • module paths are relative to the tested module not the test file
  • therefore specify it exactly as in the require statement inside the tested file
  • values themselves are key/value pairs of functions/properties and the appropriate override

Preventing call thru to original dependency

By default proxyquire calls the function defined on the original dependency whenever it is not found on the stub.

If you prefer a more strict behavior you can prevent callThru on a per module or global basis.

Prevent call thru on path stub:

var foo = proxyquire.resolve('./foo', __dirname, {
  path: { 
      extname: function (file) { ... } 
    , '@noCallThru': true
  }
});

Prevent call thru for all future stubs:

proxyquire.noCallThru();

Re-enable call thru for all future stubs:

proxyquire.noCallThru(false);

Call thru config per module wins:

var foo = proxyquire
    .noCallThru()
    .resolve('./foo', __dirname, {

        // no calls to original './bar' methods will be made
        './bar' : { toAtm: function (val) { ... } }

        // for 'path' module they will be made
      , path: { 
          extname: function (file) { ... } 
        , '@noCallThru': false
        }
    });

Changing the TmpDir

proxyquire.tmpDir({string} tmpdir)

In order to hook into your code, proxyquire writes some intermediate files into the tmp directory.

By default it will use the TMPDIR of your environment, but this method allows you to override it.

Examples

We are testing foo which depends on bar:

// bar.js module
module.exports = { 
    toAtm: function (val) { return  0.986923267 * val; }
};

// foo.js module 
// requires bar which we will stub out in tests
var bar = require('./bar');
[ ... ]

Tests:

// foo-test.js module which is one folder below foo.js (e.g., in ./tests/)

/*
 *   Option a) Resolve and override in one step:
 */
var foo = proxyquire.resolve('../foo', __dirname, {
  './bar': { toAtm: function (val) { return 0; /* wonder what happens now */ } }
});

// [ .. run some tests .. ]

/*
 *   Option b) Resolve with empty stub and add overrides later
 */
var barStub = { };

var foo =  proxyquire.resolve('../foo', __dirname, { './bar': barStub }); 

// Add override
bar.toAtm = function (val) { return 0; /* wonder what happens now */ };

[ .. run some tests .. ]

// Change override
bar.toAtm = function (val) { return -1 * val; /* or now */ };

[ .. run some tests .. ]

// Resolve foo and override multiple of its dependencies in one step - oh my!
var foo = proxyquire.resolve('./foo', __dirname, {
    './bar' : { 
      toAtm: function (val) { return 0; /* wonder what happens now */ } 
    }
  , path    : { 
      extname: function (file) { return 'exterminate the name of ' + file; } 
    }
});

More Examples

For more examples look inside the examples folder or look through the tests

For an example on how to use proxyquire with Sinon.JS, look in here.