Add FactoryGirl integration

Introduce optional FactoryGirl syntax that makes it easier to use
Formulaic to fill in attributes from a factory with a single argument:
`fill_with_factory(:user)`; limit the attributes from a factory:
`fill_with_factory(:user, :name, :address)`; and even pass arguments to
the factory, such as traits and overrides:
`fill_with_factory(:user, :name, :address, factory_arguments: [:with_verified_address]`.

Resolves #11.

README.md

@@ -90,19 +90,35 @@ end
 ### Integration with [FactoryGirl](https://github.com/thoughtbot/factory_girl)
 
 ```ruby
-fill_form(:user, attributes_for(:user))
+require 'formulaic/factory_girl'
+
+fill_with_factory(:user, attributes_for(:user))
 ```
 
 You may have attributes included in your `User` factory that don’t pertain to
 sign up:
 
 ```ruby
-fill_form(:user, attributes_for(:user).slice(sign_up_attributes))
+require 'formulaic/factory_girl'
 
-# ...
-def sign_up_attributes
-  [:name, :email, :terms_of_service]
-end
+fill_with_factory(:user, :name, :email, :terms_of_service)
+```
+
+If you need to pass specific arguments to the factory, such as [traits] or to
+override values, pass them in the `factory_arguments` parameter.
+
+[traits]: https://github.com/thoughtbot/factory\_girl/blob/master/GETTING\_STARTED.md#traits
+
+```ruby
+require 'formulaic/factory_girl'
+
+fill_with_factory(:user, factory_arguments: [:registered, name: 'Frank'])
+```
+
+Which is roughly equivalent to calling:
+
+```ruby
+fill_form(:user, attributes_for(:user, :registered, name: 'Frank'))
 ```
 
 ## Assumptions

formulaic.gemspec

@@ -29,4 +29,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rake'
   spec.add_development_dependency 'rspec'
   spec.add_development_dependency 'pry'
+  spec.add_development_dependency 'factory_girl'
 end

lib/formulaic/factory_girl.rb

@@ -0,0 +1,25 @@
+require 'formulaic/dsl'
+require 'factory_girl'
+require 'active_support/concern'
+
+module Formulaic
+  module FactoryGirl
+    include ::FactoryGirl::Syntax::Methods
+    def fill_with_factory(model_name, *attribute_whitelist, factory_arguments: [])
+      attributes = attributes_for(model_name, *factory_arguments)
+
+      if attribute_whitelist.any?
+        attributes = attributes.slice(*attribute_whitelist)
+      end
+
+      fill_form(model_name, attributes)
+    end
+  end
+
+  Formulaic::Dsl.send(:include, Formulaic::FactoryGirl)
+end
+
+#fill_with_factory(:user, :name, :age, factory_arguments: [:authenticated, :super_old, name: 'george'])
+#=>
+#Formulaic::Dsl.fill_form(FactoryGirl.attributes_for(:user, :authenticated, :super_old, name: 'george').slice(:name, :age))
+

spec/formulaic/factory_girl_spec.rb

@@ -0,0 +1,62 @@
+require 'spec_helper'
+require 'formulaic/factory_girl'
+
+describe Formulaic::FactoryGirl, :factory_girl do
+  before(:all) do
+    define_user_factory(user_class)
+  end
+
+  after(:all) do
+    FactoryGirl.factories.clear
+  end
+
+  it 'sets attributes to FactoryGirl.attributes_for(model_name) if attributes is omitted' do
+    allow(class_with_dsl).to receive(:fill_form)
+
+    fill_with_factory(:user)
+
+    expect(class_with_dsl).to have_received(:fill_form).with(:user, FactoryGirl.attributes_for(:user))
+  end
+
+  it 'slices the attributes if an attribute whitelist is included' do
+    allow(class_with_dsl).to receive(:fill_form)
+
+    fill_with_factory(:user, :name)
+
+    expect(class_with_dsl).to have_received(:fill_form).with(:user, FactoryGirl.attributes_for(:user).slice(:name))
+  end
+
+  it 'merges overrides into the attributes' do
+    allow(class_with_dsl).to receive(:fill_form)
+
+    fill_with_factory :user, :name, factory_arguments: [name: 'Tao' ]
+
+    expect(class_with_dsl).to have_received(:fill_form).with(:user, { name: 'Tao' })
+  end
+
+  delegate :fill_with_factory, to: :class_with_dsl
+
+  def class_with_dsl
+    @class ||= Class.new { include Formulaic::Dsl }.new
+  end
+
+  def user_class
+    @user ||= Class.new do
+      attr_accessor :name, :age
+
+      def initialize(options)
+        @name = options[:name]
+        @age = options[:age]
+      end
+    end
+  end
+
+  def define_user_factory(user_class)
+    FactoryGirl.define do
+      factory :user, class: user_class do
+        name 'Roen Tan'
+        age 31
+      end
+    end
+  end
+end

spec/spec_helper.rb

@@ -1,6 +1,8 @@
 require 'formulaic'
 require 'pry'
 
+I18n.enforce_available_locales = false
+
 module SpecHelper
   def input(model, field)
     page.find("##{model}_#{field}")
@@ -37,4 +39,5 @@ def load_translations
 
 RSpec.configure do |c|
   c.include SpecHelper
+  c.treat_symbols_as_metadata_keys_with_true_values = true
 end