Run Rake and Rails commands during a development console session and run tests during a test console session. This side-steps the need to load the entire environment over and over again when you run these commands from the shell. This constant reloading of the environment is what causes slow boot time on big applications. Think of this like a baby Zeus or the Turbolinks of commands.
Add this line to your application's Gemfile:
gem 'commands'
And then execute:
$ bundle
When your console boots, it'll automatically have a commander object instantiated. The following methods are delegated to this object: rake, generate, destroy, update. It's used like this:
> generate "scaffold post title:string"
> rake "db:migrate"
To use a persistent console for testing, be sure to first start it in the test environment, like so ./script/rails console test. Then you can run tests like this:
> test "models"
> test "controllers"
> test "models/person"
You can see the options available for all the commands by running them with no parameters.