title: Mocha can't find modules in imported code
body: <p>I have a Phoenix app and am trying to get Mocha wired up for javascript unit tests. I want to test module 'Two', that imports module 'One' but I can't figure out how to configure Mocha to find module one.  </p>
  
  <p>Here is the test code:</p>
  
  <blockquote>
    <p><em>web/static/js/one.js</em></p>
  </blockquote>
  
  <pre><code>export var One = 1;
  </code></pre>
  
  <blockquote>
    <p><em>web/static/js/two.js</em></p>
  </blockquote>
  
  <pre><code>import {One} from "web/static/js/one";
  export var Two = function () {return One + One;}
  </code></pre>
  
  <p><em>> test/js/two_test.js</em></p>
  
  <pre><code>import assert from 'assert';
  import {Two} from "../../web/static/js/two";
  
  describe('Two()', function() {
    it('returns value 2', function () {
      assert.equal(2, Two());
    });
  });
  </code></pre>
  
  <p>Here is the output when I run <code>npm test</code></p>
  
  <pre><code>home:~/elixir/optitrue$ npm test
  
  &gt; @ test /home/jon/elixir/optitrue
  &gt; mocha --compilers js:babel-register test/js/**/*.js
  
  module.js:457
      throw err;
      ^
  
  Error: Cannot find module 'web/static/js/one'
      at Function.Module._resolveFilename (module.js:455:15)
      at Function.Module._load (module.js:403:25)
      at Module.require (module.js:483:17)
      at require (internal/module.js:20:19)
      at Object.&lt;anonymous&gt; (two.js:1:1)
      at Module._compile (module.js:556:32)
      at loader (/home/jon/elixir/optitrue/node_modules/babel-register/lib/node.js:148:5)
      at Object.require.extensions.(anonymous function) [as .js] (/home/jon/elixir/optitrue/node_modules/babel-register/lib/node.js:158:7)
      at Module.load (module.js:473:32)
      at tryModuleLoad (module.js:432:12)
      at Function.Module._load (module.js:424:3)
      at Module.require (module.js:483:17)
      at require (internal/module.js:20:19)
      at Object.&lt;anonymous&gt; (two_test.js:2:1)
      at Module._compile (module.js:556:32)
      at loader (/home/jon/elixir/optitrue/node_modules/babel-register/lib/node.js:148:5)
      at Object.require.extensions.(anonymous function) [as .js] (/home/jon/elixir/optitrue/node_modules/babel-register/lib/node.js:158:7)
      at Module.load (module.js:473:32)
      at tryModuleLoad (module.js:432:12)
      at Function.Module._load (module.js:424:3)
      at Module.require (module.js:483:17)
      at require (internal/module.js:20:19)
      at /home/jon/elixir/optitrue/node_modules/mocha/lib/mocha.js:220:27
      at Array.forEach (native)
      at Mocha.loadFiles (/home/jon/elixir/optitrue/node_modules/mocha/lib/mocha.js:217:14)
      at Mocha.run (/home/jon/elixir/optitrue/node_modules/mocha/lib/mocha.js:485:10)
      at Object.&lt;anonymous&gt; (/home/jon/elixir/optitrue/node_modules/mocha/bin/_mocha:403:18)
      at Module._compile (module.js:556:32)
      at Object.Module._extensions..js (module.js:565:10)
      at Module.load (module.js:473:32)
      at tryModuleLoad (module.js:432:12)
      at Function.Module._load (module.js:424:3)
      at Module.runMain (module.js:590:10)
      at run (bootstrap_node.js:394:7)
      at startup (bootstrap_node.js:149:9)
      at bootstrap_node.js:509:3
  </code></pre>
  
  <blockquote>
    <p>brunch.config</p>
  </blockquote>
  
  <pre><code>exports.config = {
    // See http://brunch.io/#documentation for docs.
    files: {
      javascripts: {
        joinTo: "js/app.js"
      },
      stylesheets: {
        joinTo: "css/app.css"
      },
      templates: {
        joinTo: "js/app.js"
      }
    },
  
    conventions: {
      assets: /^(web\/static\/assets)/
    },
  
    // Phoenix paths configuration
    paths: {
      watched: [
        "web/static",
        "test/static"
      ],
  
      // Where to compile files to
      public: "priv/static"
    },
  
    // Configure your plugins
    plugins: {
      babel: {
        // Do not use ES6 compiler in vendor code
        ignore: [/web\/static\/vendor/]
      }
    },
  
    modules: {
      autoRequire: {
        "js/app.js": ["web/static/js/app"]
      }
    },
  
    npm: {
      enabled: true,
      whitelist: ["phoenix", "phoenix_html"]
    }
  };
  </code></pre>