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Proxies nodejs require in order to allow overriding dependencies during testing.

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


  • no changes to your code are necessary
  • non overriden methods of a module behave like the original
  • mocking framework agnostic, if it can stub a function then it works with proxyquire
  • "use strict" compliant



var path = require('path');

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

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


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


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


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.

If callThru is disabled, you can stub out modules that don't even exist on the machine that your tests are running on. While I wouldn't recommend this in general, I have seen cases where it is legitimately useful (e.g., when requiring global environment configs in json format that may not be available on all machines).

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:


Re-enable call thru for all future stubs:


Call thru config per module wins:

var foo = proxyquire
    .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.


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');
[ ... ]


// 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

Specific Examples:

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