如何在Mocha测试中模拟全局变量(定义，模块，窗口)? [英] How to mock global variables (define, module, window) in mocha tests?

问题描述

为了追求100％的代码覆盖率，我尝试使用mocha来测试我的javascript模块是否在 AMD ， CommonJS/Node 下正确加载，和 browser 条件.我正在使用的模式如下:

In the pursuit of 100% code coverage, I am attempting to use mocha to test that my javascript module is loading correctly under AMD, CommonJS/Node, and browser conditions. The pattern I'm using is below:

my-module.js

(function(global){

  function MyClass(){}

  // AMD
  if(typeof define === 'function' && define.amd){
    define(function(){
      return MyClass;
    });

  // CommonJS/Node
  } else if (typeof module !== 'undefined' && module.exports){
    module.exports = MyClass;

  // Browser
  } else {
    global.MyClass = MyClass;
  }

})(this);

由于我正在使用节点运行测试，因此从未定义define，并且始终定义了module.因此"CommonJS/Node"条件是唯一经过测试的条件.

Since I am running my tests with node, define is never defined, and module is always defined; so the "CommonJS/Node" condition is the only one that ever gets tested.

到目前为止，我尝试过的事情是这样的:

What I have tried so far is something like this:

my-module.test.js

var MyClass = require('./my-module');

describe('MyClass', function(){
  // suite of tests for the class itself
  // uses 'var instance = new MyClass();' in each test
  // all of these tests pass
});

describe('Exports', function(){
  // suite of tests for the export portion
  beforeEach(function(){
    MyClass = null; // will reload module for each test
    define = null; // set 'define' to null
    module = null; // set 'module' to null
  });

  // tests for AMD
  describe('AMD', function(){
    it('should have loaded as AMD module', function(){
      var define = function(){};
      define.amd = true;

      MyClass = require('./my-module'); // might be cached?
      // hoping this reloads with 'define' in its parent scope
      // but it does not. AMD condition is never reached.

      expect(spy).to.have.been.called(); // chai spy, code omitted
    });
  });
});

我正在使用间谍程序检查define是否已被调用，但是该模块未显示任何可用的define重新加载的迹象.我该如何实现?

I'm using spies to check if define has been called, but the module doesn't show any signs of ever being reloaded with define available to it. How can I achieve that?

并且有一种安全的方法来取消module以便我也可以测试浏览器条件吗?

And is there a safe way of nullifying module so that I can test the browser condition as well?

推荐答案

我能够创建一个自定义解决方案(从

I was able to create a custom solution (borrowing the majority of this code from http://howtonode.org/testing-private-state-and-mocking-deps)

module-loader.js

此模块基本上会创建一个新的上下文，在该上下文中，您的自定义属性可在与require和console等相同的全局空间中使用.

This module basically creates a new context in which your custom properties are available in the same global space as require and console, etc.

var vm = require('vm');
var fs = require('fs');
var path = require('path');
var extend = require('extend'); // install from npm

/**
 * Helper for unit testing:
 * - load module with mocked dependencies
 * - allow accessing private state of the module
 *
 * @param {string} filePath Absolute path to module (file to load)
 * @param {Object=} mocks Hash of mocked dependencies
 */
exports.loadModule = function(filePath, mocks) {
  mocks = mocks || {};

  // this is necessary to allow relative path modules within loaded file
  // i.e. requiring ./some inside file /a/b.js needs to be resolved to /a/some
  var resolveModule = function(module) {
    if (module.charAt(0) !== '.') return module;
    return path.resolve(path.dirname(filePath), module);
  };

  var exports = {};
  var context = {
    require: function(name) {
      return mocks[name] || require(resolveModule(name));
    },
    console: console,
    exports: exports,
    module: {
      exports: exports
    }
  };

  var extendMe = {};
  extend(true, extendMe, context, mocks);

  // runs your module in a VM with a new context containing your mocks
  // http://nodejs.org/api/vm.html#vm_vm_runinnewcontext_code_sandbox_filename
  vm.runInNewContext(fs.readFileSync(filePath), extendMe);

  return extendMe;
};

my-module.test.js

var loadModule = require('./module-loader').loadModule;

// ...

it('should load module with mocked global vars', function(){
  function mockMethod(str){
    console.log("mock: "+str);
  }

  var MyMockModule = loadModule('./my-module.js', {mock:mockMethod});
  // 'MyClass' is available as MyMockModule.module.exports
});

my-module.js

(function(global){

  function MyClass(){}

  if(typeof mock !== 'undefined'){ 
    mock("testing"); // will log "mock: testing"
  }

  module.exports = MyClass;

})(this);

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