A minimal test runner for both server- and client-side JavaScript
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Logan: a minimal test runner for both server- and client-side JavaScript


Prerequisites: Logan requires Node.js. (http://nodejs.org/)

Get Logan:

git clone git://github.com/mde/logan.git

Build Logan:

cd logan && make && sudo make install

Basic usage

logan [browser|node|racer] 


Logan is a minimal test runner for both client- and
server-side JavaScript. It uses the Node.js assert library.

Logan supports the following envrironments: 
    * Browsers (via HTTP global-eval/script-append) 
    * Node.js
    * TheRubyRacer

Test syntax

A Logan test file looks like this:

var testNamespace = new function () {
  this.testFoo = function () {

  this.testBar = function () {
    assert.equal(1, 1);



Pretty simple.

Sharing client- and server-side JavaScript code and tests

For Logan's testing purposes, "server-side" means in Node.js, which uses CommonJS modules. "Client-side" includes the browsers, and TheRubyRacer, where there is no facility for loading code modules from within the runtime.

There are a few simple rules to follow when creating a module to use both in client and server:

  1. Name your namespace object in side the module file the same name as the variable you'll be setting it to when you load it via CommonJS require.

  2. Only export your namespace in the CommonJS environment.

For example, in the module file, foo.js:

if (typeof foo != 'undefined') { foo = {}; }

foo.bar = new function () {
  this.a = 1;
  this.b = function () {};

if (typeof module != 'undefined') { module.exports = foo.bar; }

Or, if you are exporting a constructor:

if (typeof foo != 'undefined') { foo = {}; }

foo.Baz = function () {
  this.a = 2;
  this.b = [];

if (typeof exports != 'undefined') { exports.Baz = foo.Baz; }
  1. When you call require in your source code, use the same name as in the module.

  2. Create any top-level namespace objects non-destructively.

In your tests, if you're creating top-level namespaces to hang your required objects on, use something to create them that checks for their existence before creating.

Logan includes a utility function, logan.namespace, to help with this. In your own app's code, you'll either have to use a utility function for doing this, or simply check with a typeof check for undefined.

Here's how to load and use the previous two examples:

foo.bar = require('./path/to/foo');
foo.Bar = require('./path/to/bar').Bar;

var fooTests = new function () {
  this.testFooBarAIsTruthy = function () {

  this.testFooBazAIsNumber = function () {
    var barInstance = new foo.Bar();
    assert.equal(typeof barInstance.a, 'number');



The reason for these special requirements is the difference between the way that code loads on the client and the way it loads via CommonJS.

In the client environment (including TheRubyRacer), there is no module-level scope, and the mechanism for loading code doesn't return any value, so namespace creation has to happen inside the module file, and has to be careful not to rewrite anything other modules might have done.

Logan makes this work with CommonJS require syntax in your tests by doing source-code transformation -- it uses the require statements to know what code to load, and rewrites the statements so they don't stomp on the results of the eval operation.


Matthew Eernisse, mde@fleegix.org