Mocha runs independently from the [assertion library](http://visionmedia.github.io/mocha/#assertions), so you can choose which assertion format works best for you. Mocha most often is run in combination with assertion library [Chai](http://chaijs.com).
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Pro Configurations are easy to write
Grunt emphasizes configuration over code. As such grunt configurations are easy to write. Writing them does not require knowledge of streams, promises, concurrency, or asynchronous tasks to set up.
Pro Has tons of plugins
Grunt has been available for a long time and during this time it has garnered a large community of dedicated developers who have made more than 4000 grunt plugins available to be used.
Pro Plugins configured out of the box
The default behaviors for most plugins is normally what you want, so if you just use a plugin without configuring it, it will work for most use cases.
Pro A GUI front-end via spock
A graphical user interface for grunt is available via spock.
Pro Choice of using it as a config file or writing your own functions
Pro Grunt v1.0 alpha uses Orchestrator for maximum concurrency
Grunt version 1 alpha, aka grunt-next, the upcoming next major release of Grunt, uses Orchestrator to sequence and execute tasks and dependencies with maximum concurrency, potentially bringing it up to speed with Gulp in term of performance.
Pro An API that makes writing and using of plugins extremely easy
The API is built in such a way that if you write a Grunt task that is useful for someone else out there or would be useful for future projects, it can be easily made into a grunt plugin and then shared using npm.
Pro Shell commands inside Grunt
There is a Grunt plugin called grunt-exec which allows developers to execute shell commands inside their Grunt files. This is extremely easy if a developer is developing only in Node and constantly getting out of Node environment to run something like a git command can become frustrating.
Pro Write tests with Behavior Driven Development (BDD)
Allows developers to choose their development process. Not only TDD but also BDD.
Pro Makes Asynchronous testing extremely easy
No need to write tricky statements for Async testing. Mocha gives you a
done callback. Place this
done parameter in your callback function, that'll let Mocha know that you've written an asynchronous function.
Pro Integrates really well with NodeJS
The Mocha test framework itself runs on NodeJS, hence it makes everything related to it extremely simple. With Mocha's simple syntax and speed, testing your node.js app just got a whole lot easier.
Pro Runs in Node.js and the browser
Mocha has a browser build as well as a node command line program so you can test in client and server side environments.
Pro Custom full color test reporters
Mocha has multiple test reporters built in and you can create your own as well. The test reporters have full color and makes it easy to see if your tests fail or not.
Pro Easy to add support for Generators
Aside from the numerous benefits with generators in your application, You can now also integrate generators into your test suite. By using mocha, all you have to do is enable support for generators.
Con Large bloated configuration files
To configure Grunt, developers need to basically write large files and configure JSON objects. While it's very powerful, the sheer complexity of it's configuration file may be a large obstacle for newcomers and developers that have not used any automation tools before. This may push them to search for simpler alternatives.
Con The need to track creation/movement of files
Debugging and augmenting grunt pipelines are much harder than other build systems that clearly show the pipelines in the code.
Grunt works on files so you must track where each task puts files and try and intercept that in a task if you want to add something in the middle of a build pipeline.
Con Grunt compatibility issues
Changes in different versions in grunt are not always backwards-compatible.
Con No atomic tests
Tests cannot be ran in random order.
Con Can be intimidating for beginners
While some testing frameworks are complete out of the box, Mocha requires developers to select and set up assertion libraries and mocking utilities. For someone who is just starting to learn how to build tests this can be scary as they will also have to choose which libraries to use and learn them too.