We are preferring Factory Girl Gem to simulate the application related test data.

What is Factory Girl?

A library for setting up Ruby objects as test data, a replacement for Fixtures.

Factories allow you to create valid instances of your Rails model classes to reuse. Factories are commonly used to DRY out unit tests.

Transient Attributes

  • Customize your factory behaviour with fake/virtual attributes.
  • These attributes are just parameters to the factory method call that can be used by your code inside the factory.

Now, let’s see the following example.

factory :post do
  transient do
    approved false

  title { approved ? "This is my first post" : "Admin, please approve this post" }

#=> "Admin, please approve this post"

create(:post, approved: true).title
#=> "This is my first post"

In the above example, approved is a fake/virtual attribute which does not belong to Post model & we are creating title of the Post on the basis of this transient attribute’s value.

Note: In the older versions, it is also known as ignored attributes. The old ignore syntax has been deprecated and removed from Factory Girl version 3.0 onwards.