How to get an application to use a local branch version of Ruby on Rails

Let's say I want to add some new features to Ra开发者_开发问答ils. According to the Rails Guide on how to contribute to Rails, I should clone the main repository, create a branch, then make my changes in that branch.

My question is: after I've done all of that, how do I go about testing my changes in an actual Rails application? That is, how do I get a Rails application running on my machine to use the Rails code from my branch rather than the Rails code installed on my system?

The simplest approach I can think of is to simply replace the "rails" folder in my gems folder with the code from my branch, but it seems like there should be a cleaner way to do this.

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If you're using bundler, just point to your modified version in your Gemfile by specifying either the path of the gem on the filesystem or your forked git repo. Like this:

gem 'rails', :path => '/full/path/to/mofidied/rails'

or for git:

gem 'rails', :git => git://github.com/github_user/your_rails.git

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If you change the minor revision number and install it in your gems folder you can specify that new version when you create a new app

rails _3.0.x_ new newappname