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.

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Installation

npm install rewire

For older node versions

rewire is tested with node 0.6.x. I recommend to run the unit tests via mocha in the rewire-folder before using rewire with older node versions.

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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"];

// This will inject
// module.exports._ = {myPrivateVar1: myPrivateVar1, myPrivateVar2: myPrivateVar2}
// at the bottom of the module.
rewiredModule = rewire("./myModuleA.js", null, null, leaks);

// You now can access your private varialbes under the special __-object
rewiredModule.__.myPrivateVar1; // returns former private variable myPrivateVar1
rewiredModule.__.myPrivateVar2; // returns former private variable 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.

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##API

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

• {!String} filename:
  Path to the module that shall be rewired. Use it exactly like require().

• {Object} mocks (optional):
  An object with mocks.

• {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.

• {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.

Returns the rewired module.

rewire.reset()

Removes all rewired modules from require.cache. Every require() will now return the original module again.

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Please note

mocks

Keys should be 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}.

injections

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.

Imagine rewire("./myModule.js", null, {console: null});:

console.log("Hello");   // ouch, that won't work. console is undefined at this point because of hoisting

// End of module ///////////////
// rewire will inject here
var console = null;

leaks

Leaks are executed at the end of the module. If a var is undefined at this point you won't be able to access the leak (because undefined-values are copied by value). A good approach to this is:

var myLeaks = {};

module.exports = function (someValue) {
   myLeaks.someValue = someValue;
};

// End of module ///////////////
// rewire will inject here
module.exports.__ = {myLeaks: myLeaks};

Because myLeaks is defined at the end of the module, you're able to access the leak object and all leaks that are attached to it later during runtime. Because myLeaks is not exposed under regular circumstances your module interface stays clean.

reset

You should call this before every unit test to ensure a clean test environment.

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Credits

This module is inspired by the great injectr-module.

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License

(The MIT License)

Copyright (c) 2012 Johannes Ewald <[email protected]>

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.