Object Daddy

Version 0.4.2 (July 28, 2009)

Authors: Rick Bradley, Yossef Mendelssohn

Copyright: Copyright (c) 2007, Flawed Logic, OG Consulting, Rick Bradley, Yossef Mendelssohn

License: MIT License. See MIT-LICENSE file for more details.

Object Daddy is a library (as well as a Ruby on Rails plugin) designed to assist in automating testing of large collections of objects, especially webs of ActiveRecord models. It is a descendent of the "Object Mother" pattern for creating objects for testing, and is related to the concept of an "object exemplar" or stereotype.

WARNING This code is very much at an alpha development stage. Usage, APIs, etc., are all subject to change.

See http://b.logi.cx/2007/11/26/object-daddy for inspiration, historical drama, and too much reading.

Presuming your version of Rails has git plugin installation support:

script/plugin install git://github.com/flogic/object_daddy.git

Otherwise, you can install object_daddy by hand:

1. Unpack the object_daddy directory into vendor/plugins/ in your rails project.
2. Run the object_daddy/install.rb Ruby script.

Install the rspec gem and cd into the object_daddy directory. Type spec spec/ and you should see all specs run successfully. If you have autotest from the ZenTest gem installed you can run autotest in that directory.

Object Daddy adds a .generate method to every ActiveRecord model which can be called to generate a valid instance object of that model class, for use in testing:

it "should have a comment for every forum the user posts to" do
  @user = User.generate
  @post = Post.generate
  @post.comments << Comment.generate
  @user.should have(1).comments
end

This allows us to generate custom model objects without relying on fixtures, and without knowing, in our various widespread tests and specs, the details of creating a User, Post, Comment, etc. Not having to know this information means the information isn't coded into dozens (or hundreds) of tests, and won't need to be changed when the User (Post, Comment, ...) model is refactored later.

Object Daddy will identify associated classes that need to be instantiated to make the main model valid. E.g., given the following models:

class User < ActiveRecord::Base
  belongs_to :login
  validates_presence_of :login
end

class Login < ActiveRecord::Base
  has_one :user
end

A call to User.generate will also make a call to Login.generate so that User#login is present, and therefore valid.

If all models were able to be created in a valid form by the default Model.new call with no knowledge of the model itself, there'd be no need for Object Daddy. So, when we deal with models which have validity requirements, requiring fields which have format constraints, we need a means of expressing how to create those models -- how to satisfy those validity constraints.

Object Daddy provides a generator_for method which allows the developer to specify, for a specific model attribute, how to make a valid value. Note that validates_uniqueness_of can require that, even if we make 100,000 instances of a model that unique attributes cannot have the same values.

Object Daddy's generator_for method can take three main forms corresponding to the means of finding a value for the associated attribute: a block, a method call, or using a generator class.

class User < ActiveRecord::Base
  validates_presence_of :email
  validates_uniqueness_of :email
  validates_format_of :email, 
  :with => /^[-a-z_+0-9.]+@(?:[-a-z_+0-9.]\.)+[a-z]+$/i
  validates_presence_of :username
  validates_format_of :username, :with => /^[a-z0-9_]{4,12}$/i

  generator_for :email, :start => 'test@domain.com' do |prev|
    user, domain = prev.split('@')
    user.succ + '@' + domain
  end

  generator_for :username, :method => :next_user

  generator_for :ssn, :class => SSNGenerator

  def self.next_user
    @last_username ||= 'testuser'
    @last_username.succ
  end
end

class SSNGenerator
  def self.next
    @last ||= '000-00-0000'
    @last = ("%09d" % (@last.gsub('-', '').to_i + 1)).sub(/^(\d{3})(\d{2})(\d{4})$/, '\1-\2-\3')
  end
end

Note that the block method of invocation (as used with :email above) takes an optional :start argument, to specify the value of that attribute on the first run. The block will be called thereafter with the previous value of the attribute and will generate the next attribute value to be used.

A simple default block is provided for any generator with a :start value.

class User < ActiveRecord::Base
  generator_for :name, :start => 'Joe' do |prev|
    prev.succ
  end

  generator_for :name, :start => 'Joe'  # equivalent to the above
end

The :method form takes a symbol naming a class method in the model class to be called to generate a new value for the attribute in question. If the method takes a single argument, it will act much like the block method of invocation, being called with the previous value and generating the next.

The :class form calls the .next class method on the named class to generate a new value for the attribute in question.

The argument (previous value) to the block invocation form can be omitted if it's going to be ignored, and simple invocation forms are provided for literal values.

class User < ActiveRecord::Base
  generator_for(:start_time) { Time.now }
  generator_for :name, 'Joe'
  generator_for :age => 25
end

The developer would then simply call User.generate when testing.

If some attribute values are known (or are being controlled during testing) then these can simply be passed in to .generate:

@bad_login = Login.generate(:expiry => 1.week.ago)
@expired_user = User.generate(:login => @bad_login)

A .generate! method is also provided. The generate/generate! pair of methods can be thought of as analogs to create/create!, one merely providing an instance that may or may not be valid and the other raising an exception if any problem comes up.

Finally, a .spawn method is provided that only gives a new, unsaved object. Note that this is the only method of the three that is available if you happen to be using Object Daddy outside of Rails.

In the examples given above we are using generator_for in the bodies of the models themselves. Given that Object Daddy is primarily geared towards annotating models with information useful for testing, we anticipate that generator_for should not normally be included inline in models. Rather, we will provide a place where model classes can be re-opened and generator_for calls (and support methods) can be written without polluting the model files with Object Daddy information.

Object Daddy, when installed as a Rails plugin, will create RAILS_ROOT/spec/exemplars/ as a place to hold exemplar files for Rails model classes. (We are seeking perhaps some better terminology)

An exemplar for the User model would then be found in RAILS_ROOT/spec/exemplars/user_exemplar.rb (when you are using a testing tool which works from RAILS_ROOT/test, Object Daddy will create RAILS_ROOT/test/exemplars and look for your exemplars in that directory instead). Exemplar files are completely optional, and no model need have exemplar files. The .generate method will still exist and be callable, and generator_for can be declared in the model files themselves. If an exemplar file is available when .generate is called on a model, the exemplar file will be loaded and used. An example user_exemplar.rb appears below:

require 'ssn_generator'

class User < ActiveRecord::Base
  generator_for :email, :start => 'test@domain.com' do |prev|
    user, domain = prev.split('@')
    user.succ + '@' + domain
  end

  generator_for :username, :method => :next_user

  generator_for :ssn, :class => SSNGenerator

  def self.next_user
    @last_username ||= 'testuser'
    @last_username.succ
  end
end

The spawn, generate and generate! methods can all accept a block, to which they'll yield the generated object. This provides a nice scoping mechanism in your code examples. Consider:

describe "admin user" do
  it "should be authorized to create company profiles"
    admin_user = User.generate!
    admin_user.activate!
    admin_user.add_role("admin")

    admin_user.should be_authorized(:create, Company)
  end
end

This could be refactored to:

describe "admin user" do
  it "should be authorized to create company profiles" do
    admin_user = User.generate! do |user|
      user.activate!
      user.add_role("admin")
    end

    admin_user.should be_authorized(:create, Company)
  end
end

Or:

describe "admin user" do
  it "should be authorized to create company profiles"
    User.generate! do |user|
      user.activate!
      user.add_role("admin")
    end.should be_authorized(:create, Company)
  end
end

Or even:

describe "admin user" do
  def admin_user
    @admin_user ||= User.generate! do |user|
      user.activate!
      user.add_role("admin")
    end
  end

  it "should be authorized to create company profiles"
    admin_user.should be_authorized(:create, Company)
  end
end

This last refactoring allows you to reuse the admin_user method across multiple code examples, balancing DRY with local data.

While Object Daddy is meant to obviate the hellish devilspawn that are test fixtures, Object Daddy should work alongside fixtures just fine. To each his own, I suppose.

The simple invocation forms for generator_for when using literal values do not work if the literal value is a Hash. Don't do that.

class User < ActiveRecord::Base
  generator_for :thing_hash, { 'some key' => 'some value' }
  generator_for :other_hash => { 'other key' => 'other value' }
end

I'm not sure why this would even ever come up, but seriously, don't.

Required belongs_to associations are automatically generated when generating an instance, but only if necessary.

class Category < ActiveRecord::Base
  has_many :items
end

class Item < ActiveRecord::Base
  belongs_to :category
  validates_presence_of :category
end

Item.generate will generate a new category, but some_category.items.generate will not. Unless, of course, you are foolish enough to define a generator in the exemplar.

class Item
  generator_for(:category) { Category.generate }
end

Once again, don't do that.

Due to the way Rails handles associations, cascading generations (as a result of required associations) are always generated-and-saved, even if the original generation call was a mere spawn (new). This may come as a surprise, but it would probably be more of a surprise if User.spawn.save and User.generate weren't comparable.