A minimal Rails 3 generator

model.rb

# lib/generators/test_generator/templates/model.rb
class <%= class_name %>
  <%- fields.each do |field| -%>

  def <%= field %>
    puts "<%= field %>"
  end
  <%- end -%>
end

test_generator_generator.rb

# lib/generators/test_generator/test_generator_generator.rb

require 'rails/generators'
require 'rails/generators/named_base'

class TestGeneratorGenerator < Rails::Generators::NamedBase
  source_root File.expand_path('../templates', __FILE__)
  argument :fields, :type => :array
  check_class_collision

  def create_model_file
    template 'model.rb', File.join('app','models', class_path, "#{file_name}.rb"
  end

  # All public methods get called when the generator is invoked
  protected
  def shouldnt_get_called
    puts "Shouldnt get called"
  end
end

test_generator_test.rb

# test/unit/test_generator_test.rb

require File.join(File.dirname(__FILE__), '..', 'test_helper')

require 'generators/test_generator/test_generator_generator'

class TestGeneratorTest < Rails::Generators::TestCase

  # Name of the generator class that this test exercises
  tests TestGeneratorGenerator

  # Generate test files in this directory
  destination File.join(Rails.root, 'tmp')

  # Set up the destination directory, removing previously generated
  # files if necessary
  setup :prepare_destination

  test "it should do its stuff" do
    # Run the generator with the given arguments, which will output
    # the results in the destination above.
    run_generator %w(Flum poop gloop)
    
    # Check the model files class name
    assert_file 'app/models/flum.rb', /class Flum/

    # Should create a method for each of the extra arguments passed
    assert_file 'app/models/flum.rb', /def poop/
    assert_file 'app/models/flum.rb', /def gloop/
  end
end

USAGE

# lib/generators/test_generator/USAGE

Description:
    A minimal rails 3 generator example

Example:
    rails generate NewClass method1 method2

    This will create:
        app/models/new_class.rb

    Which will contain the following methods:

      def method1
        puts "method1"
      end
      
      def method2
        puts "method2"
      end