Fixtures aren't fun. Machinist is.
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Fixtures aren't fun. Machinist is.

Machinist makes it easy to create test data within your tests. It generates data for the fields you don't care about, and constructs any necessary associated objects, leaving you to only specify the fields you do care about in your tests. For example:

describe Comment do
  before do
    # This will make a Comment, a Post, and a User (the author of
    # the Post), and generate values for all their attributes:
    @comment = Comment.make(:spam => true)

  it "should not include comments marked as spam in the without_spam named scope" do
    Comment.without_spam.should_not include(@comment)

You tell Machinist how to do this with blueprints:

require 'machinist/active_record'
require 'sham'
require 'faker'  { } { }
Sham.title { Faker::Lorem.sentence }
Sham.body  { Faker::Lorem.paragraph }

User.blueprint do

Post.blueprint do

Comment.blueprint do
  author_name  { }
  author_email { }

Download & Install

Installing as a Rails plugin

./script/plugin install git://

Installing as a Gem

sudo gem install machinist --source

Setting up your project

Create a blueprints.rb file to hold your blueprints in your test (or spec) directory. It should start with:

require 'machinist/active_record'
require 'sham'

Substitute data_mapper for active_record if that's your weapon of choice.

Require blueprints.rb in your test_helper.rb (or spec_helper.rb):

require File.expand_path(File.dirname(__FILE__) + "/blueprints")

Set Sham to reset before each test. In the class Test::Unit::TestCase block in your test_helper.rb, add:

setup { Sham.reset }

or, if you're on RSpec, in the Spec::Runner.configure block in your spec_helper.rb, add:

config.before(:all)    { Sham.reset(:before_all)  }
config.before(:each)   { Sham.reset(:before_each) }


Sham - Generating Attribute Values

Sham lets you generate random but repeatable unique attributes values.

For example, you could define a way to generate random names as: { (1..10).map { ('a'..'z').to_a.rand } }

Then, to generate a name, call:

So why not just define a helper method to do this? Sham ensures two things for you:

  1. You get the same sequence of values each time your test is run
  2. You don't get any duplicate values

Sham works very well with the excellent Faker gem by Benjamin Curtis. Using this, a much nicer way to generate names is: { }

Sham also supports generating numbered sequences if you prefer. {|index| "Name #{index}" }

If you want to allow duplicate values for a sham, you can pass the :unique option:

Sham.coin_toss(:unique => false) { rand(2) == 0 ? 'heads' : 'tails' }

You can create a bunch of sham definitions in one hit like this:

Sham.define do
  title { Faker::Lorem.words(5).join(' ') }
  name  { }
  body  { Faker::Lorem.paragraphs(3).join("\n\n") }

Blueprints - Generating Objects

A blueprint describes how to generate an object. The idea is that you let the blueprint take care of making up values for attributes that you don't care about in your test, leaving you to focus on the just the things that you're testing.

A simple blueprint might look like this:

Post.blueprint do
  title  { Sham.title }
  author { }
  body   { Sham.body }

You can then construct a Post from this blueprint with:


When you call make, Machinist calls, then runs through the attributes in your blueprint, calling the block for each attribute to generate a value. The Post is then saved and reloaded. An exception is thrown if Post can't be saved.

You can override values defined in the blueprint by passing a hash to make:

Post.make(:title => "A Specific Title")

If you don't supply a block for an attribute in the blueprint, Machinist will look for a Sham definition with the same name as the attribute, so you can shorten the above blueprint to:

Post.blueprint do
  author { }

If you want to generate an object without saving it to the database, replace make with make_unsaved. (make_unsaved also ensures that any associated objects that need to be generated are not saved. See the section on associations below.)

You can refer to already assigned attributes when constructing a new attribute:

Post.blueprint do
  author { }
  body   { "Post by #{author}" }

Named Blueprints

Named blueprints let you define variations on an object. For example, suppose some of your Users are administrators:

User.blueprint do

User.blueprint(:admin) do
  name  { + " (admin)" }
  admin { true }



will use the :admin blueprint.

Named blueprints call the default blueprint to set any attributes not specifically provided, so in this example the email attribute will still be generated even for an admin user.

Belongs_to Associations

If you're generating an object that belongs to another object, you can generate the associated object like this:

Comment.blueprint do
  post { Post.make }

Calling Comment.make will construct a Comment and its associated Post, and save both.

If you want to override the value for post when constructing the comment, you can do this:

post = Post.make(:title => "A particular title)
comment = Comment.make(:post => post)

Machinist will not call the blueprint block for the post attribute, so this won't generate two posts.

Machinist is smart enough to look at the association and work out what sort of object it needs to create, so you can shorten the above blueprint to:

Comment.blueprint do

Other Associations

For has_many and has_and_belongs_to_many associations, ActiveRecord insists that the object be saved before any associated objects can be saved. That means you can't generate the associated objects from within the blueprint.

The simplest solution is to write a test helper:

def make_post_with_comments(attributes = {})
  post = Post.make(attributes)
  3.times { post.comments.make }

Note here that you can call make on a has_many association. (This isn't yet supported for DataMapper.)

Make can take a block, into which it passes the constructed object, so the above can be written as:

def make_post_with_comments
  Post.make(attributes) do |post|
    3.times { post.comments.make }

Using Blueprints in Rails Controller Tests

The plan method behaves like make, except it returns a hash of attributes, and doesn't save the object. This is useful for passing in to controller tests:

test "should create post" do
  assert_difference('Post.count') do
    post :create, :post => Post.plan
  assert_redirected_to post_path(assigns(:post))

plan will save any associated objects. In this example, it will create an Author, and it knows that the controller expects an author_id attribute, rather than an author attribute, and makes this translation for you.

You can also call plan on has_many associations, making it easy to test nested controllers:

test "should create comment" do
  post = Post.make
  assert_difference('Comment.count') do
    post :create, :post_id =>, :comment => post.comments.plan
  assert_redirected_to post_comment_path(post, assigns(:comment))

(Calling plan on associations is not yet supported in DataMapper.)

Blueprints on Plain Old Ruby Objects

Machinist also works with plain old Ruby objects. Let's say you have a class like:

class Post
  attr_accessor :title
  attr_accessor :body

You can then do the following in your blueprints.rb:

require 'machinist/object'

Post.blueprint do
  title "A title!"
  body  "A body!"


You can always find the latest version on GitHub.

If you have questions, check out the Google Group.

File bug reports and feature requests in the issue tracker.


Machinist is maintained by Pete Yandell (, @notahat)

Other contributors include:

Marcos Arias, Jack Dempsey, Clinton Forbes, Perryn Fowler, Niels Ganser, Jeremy Grant, Jon Guymon, James Healy, Evan David Light, Chris Lloyd, Adam Meehan, Kyle Neath, Lawrence Pit, T.J. Sheehy, Roland Swingler, Gareth Townsend, Matt Wastrodowski, Ian White

Thanks to Thoughtbot's Factory Girl. Machinist was written because I loved the idea behind Factory Girl, but I thought the philosophy wasn't quite right, and I hated the syntax.