How To Create and Test a Ruby on Rails Plugin

I’ve been learning how to create a plugin in Ruby on Rails 3.1 and test it using RSpec. I haven’t been able to find a tutorial for this anywhere, so I’ll share what I’ve done here.

First up, use rails to generate a new plugin.

$ rails generate plugin HelloWorld

This will create a folder in /vendor/plugins/hello_world containing template files for the plugin. What it won’t do is create a test file for RSpec, so we’ll create it manually later. This is a known issue.

In the plugin folder there’s a few files, most of which are self-explanatory. We’re only going to be interested in hello_world/init.rb and hello_world/lib/hello_world.rb.

hello_world/init.rb tells Rails what to do with the plugin. We’re not going to do too much, so we just need to require the main class file.

# Include hook code here
require 'hello_world'

Next we create the main class in hello_world/lib/hello_world.rb.

# HelloWorld
class HelloWorld
end

Before we go any further we should set up a test, because we do things properly. RSpec tests live in /spec so we’ll create a folder for plugin tests and create a spec file for our plugin there.

$ mkdir /spec/plugins
$ touch /spec/plugins/hello_world_spec.rb

Lets define a simple test for our plugin in /spec/plugins/hello_world_spec.rb

require 'spec_helper'
describe HelloWorld do
  describe "should have method" do
    it "'hi'" do
      response = HelloWorld.instance_methods.include? :hi
      response.should == true
    end
  end
end

We’ve done a few things here, firstly we’ve required the RSpec helper file, all RSpec tests need this. The first describe block is defined with the name of the class we are testing. Then we’ve added a test to check that a method exists. If you run the test, it should fail.

$ rspec /spec/plugins/hello_world_spec.rb

Now we can add a method to the HelloWorld class, which should get the test to pass.

# HelloWorld
class HelloWorld
  def hi
    "Hello World!"
  end
end

That’s it!

Now you have a working plugin, you can use it in your Rails application. You can create objects in controllers and call functions from views, there’s no need to explicitly require the plugin anywhere.

# app/controllers/pages_controller.rb
class PagesController < ApplicationController
  def hello
    @hw = HelloWorld.new
  end
end

<!-- app/views/pages/hello.html.erb -->
<p><%= @hw.hi %></p>