rewire

Dependency injection for node.js applications.

rewire allows you to modify the behaviour of modules for better unit testing. You may

provide mocks for other modules
leak private variables
override variables within the module
inject your own scripts

rewire does not load the file and eval the contents to emulate node's require mechanism. In fact it uses node's own require to load the module. Thus your module behaves exactly the same in your test environment as under regular circumstances (except your modifications).

Debugging is fully supported.

Installation

npm install rewire

Examples

var rewire = require("rewire"),
    rewiredModule;

// Default
////////////////////////////////
// rewire acts exactly like require when omitting all other params
rewire("./myModuleA.js") === require("./myModuleA.js"); // = true



// Mocks
////////////////////////////////
var mockedModuleB = {},
    mockedFs = {},
    mocks = {
        "fs": mockedFs,
        "path/to/moduleB.js": mockedModuleB
    };

// The rewired module will now use your mocks instead of fs
// and moduleB.js. Just make sure that the path is exactly as
// in myModuleA.js required.
rewiredModule = rewire("./myModuleA.js", mocks);



// Injections
////////////////////////////////
var injections = {
        console: {
            log: function () { /* be quiet */ }
        },
        process: { argv: ["someArgs"] },
        __filename: "some/other/dir"
    };

// This will inject
// var console = {log: function () { /* be quiet */ }};
// var process = {argv: ["someArgs"] };
// var __filename = "some/other/dir";
// at the bottom of the module.
// This way you can override private variables within the module
rewiredModule = rewire("./myModuleA.js", null, injections);

// You can also pass a script to inject
rewiredModule =
   rewire("./myModuleA.js", null, "console.log('hellooo');"); // prints "hellooo"



// Leaks
////////////////////////////////
var leaks = ["myPrivateVar1", "myPrivateVar2"];

// rewire exports variables under the special "__"-object.
rewiredModule = rewire("./myModuleA.js", null, null, leaks);
rewiredModule.__.myPrivateVar1; // returns former private myPrivateVar1
rewiredModule.__.myPrivateVar2; // returns former private myPrivateVar2



// Cache
////////////////////////////////
// By disabling the module cache the rewired module will not be cached.
// Any require()-calls will now return the original module again instead
// of the rewired. Caching is enabled by default.
rewire("./myModuleA.js", null, null, null, false) !==
    require("./myModuleA.js"); // = true

// This removes all rewired modules from require.cache.
rewire.reset();
// IMPORTANT: You should call this before every unit test to ensure
// a clean test environment.

##API

rewire(filename, mocks, injections, leaks, cache)

Returns the rewired module.

{!String} filename:
Path to the module that shall be rewired. Use it exactly like require().
{Object} mocks (optional):
An object with mocks. Keys should be the exactly the same like they're required in the target module. So if you write require("../../myModules/myModuleA.js") you need to pass {"../../myModules/myModuleA.js": myModuleAMock}.
{Object|String} injections (optional):
If you pass an object, all keys of the object will be vars within the module. You can also eval a string. Please note: All scripts are injected at the end of the module. So if there is any code in your module that is executed during require(), your injected variables will be undefined at this point. For example: passing {console: null} will cause all calls of console.log() to throw an exception if they're executed during require().
{Array<String>} leaks (optional):
An array with variable names that should be exported. These variables are accessible via myModule.__
{Boolean=true} cache (optional):
Indicates whether the rewired module should be cached by node so subsequent calls of require() will return the rewired module. Further calls of rewire() will always overwrite the cache.

rewire.reset()

Removes all rewired modules from require.cache. Every require() will now return the original module again.
Please note: You should call this before every unit test to ensure a clean test environment.

Credits

This module is inspired by the great injectr-module.

License

(The MIT License)

Copyright (c) 2012 Johannes Ewald <mail@johannesewald.de>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.