Lucky Logo

# Introduction

A Factory is a class that allows you to easily create test data.

Even though a Factory is generally used for test data, you can also use it to seed your database with development data as mentioned in database setup.

# Creating a Factory

Factories will live in your spec/support/factories/ directory. Each factory will inherit from Avram::Factory, and take the naming convention of the name of your model followed by Factory. (e.g. a User model and UserFactory)

# spec/support/factories/
class PostFactory < Avram::Factory
  def initialize
    title "My Post"
    body "Test Body"

# Factory model attributes

Each factory will have access to the associated model’s column fields. In the example PostFactory, if our Post model has a column title : String and column body : String, then the factory will have a title method and body method.

These methods take an argument of the default value you want to set for that factory.

class PostFactory < Avram::Factory
  def initialize
    title "Milk was a bad choice"
    body "Every post created from this PostFactory will default to these values"

A Post will usually have more columns like id, created_at, and updated_at. We can omit these since Avram will handle setting values on these for us. We can also omit any other fields that are nilable by default.

# Sequences

Your model may have a unique constraint on a field like a Post title, for example. In this case, you can use the sequence method to auto-increment a number on to your default value ensuring it will be unique.

class PostFactory < Avram::Factory
  def initialize
    title sequence("My new blog post")

The first time a PostFactory is created, the title will be set to "My new blog post-1". The next time one is created, the title will be set to "My new blog post-2", and so on.

Sequences always return a String. For sequence type values on other types, you’ll need to implement those yourself.

# Associations with factories

When you create a Factory, you may want to have an association already set for you. In this case, you’ll just use that association’s factory to set the foreign_key value.

class PostFactory < Avram::Factory
  def initialize
    title sequence("post-title")
    body "blah"

Creating a Factory returns an instance of that model, which means you have access to all of the model methods.

# Saving records

As shown previously, a Factory has a create method which saves the record to your database. A Factory is essentially a fancy wrapper around SaveOperation.

Factories give you access to two helpful class methods create and create_pair.

# Factory.create

This will create a Post, and store it in your database, then return the instance of Post. It will use the defaults you defined in your initialize method of PostFactory.

post = PostFactory.create
post.title #=> "post-title-1"

post2 = PostFactory.create
post2.title #=> "post-title-2"

# Overriding data

When you need to override the defaults previously set, you’ll pass a block to create.

PostFactory.create do |factory|
  factory.body("custom body")

Thanks to Crystal’s short one-argument syntax, we can shorten this with

PostFactory.create &.title("Draft").body("custom body")

# Factory.create_pair

It may be common for you to need to create more than 1 test object at a time. For this, you can use the create_pair method to create 2 test objects!.


The big difference here is that create_pair will return nil, and you can’t override the default data. Use this as “set it and forget it”.

# Testing with Factories

Once you have your factories setup, and you’re ready to test, you’ll add your tests to your spec/ directory.

# spec/
require "./spec_helper"

describe Post do
  it "has 2 posts" do

    query =
    query.should eq 2

  it "sets a custom post title" do
    post = PostFactory.create &.title("Custom Post")

    query ="Custom Post")
    query.first.should eq post

# Reloading model data

If you’ve made a change to your data, you can call reload to get the updated data.

it "updates a post title" do
  post = PostFactory.create &.title("Custom Post")

  SavePost.update!(post, title: "New Post Title")

  # The `post` still has the original data
  post.title.should eq "Custom Post"

  # Reloading returns a new model with the updated data
  updated_post = post.reload
  updated_post.title.should eq "New Post Title"

Read up on reloading models for more information.

See a problem? Have an idea for improvement? Edit this page on GitHub