- Setup
- Defining factories
- Using factories
- Aliases
- Dependent Attributes
- Transient Attributes
- Method Name / Reserved Word Attributes
- Inheritance
- Associations
- Sequences
- Traits
- Callbacks
- Modifying factories
- Building or Creating Multiple Records
- Linting Factories
- Custom Construction
- Custom Strategies
- Custom Callbacks
- Custom Methods to Persist Objects
- ActiveSupport Instrumentation
- Rails Preloaders and RSpec
- Using Without Bundler
If you're using Rails:
gem "factory_bot_rails"
If you're not using Rails:
gem "factory_bot"
If you're using Rails, add the following configuration to
spec/support/factory_bot.rb
and be sure to require that file in
rails_helper.rb
:
RSpec.configure do |config|
config.include FactoryBot::Syntax::Methods
end
If you're not using Rails:
RSpec.configure do |config|
config.include FactoryBot::Syntax::Methods
config.before(:suite) do
FactoryBot.find_definitions
end
end
class Test::Unit::TestCase
include FactoryBot::Syntax::Methods
end
# env.rb (Rails example location - RAILS_ROOT/features/support/env.rb)
World(FactoryBot::Syntax::Methods)
class Spinach::FeatureSteps
include FactoryBot::Syntax::Methods
end
class Minitest::Unit::TestCase
include FactoryBot::Syntax::Methods
end
class Minitest::Spec
include FactoryBot::Syntax::Methods
end
class ActiveSupport::TestCase
include FactoryBot::Syntax::Methods
end
If you do not include FactoryBot::Syntax::Methods
in your test suite, then all
factory_bot methods will need to be prefaced with FactoryBot
.
Each factory has a name and a set of attributes. The name is used to guess the class of the object by default:
# This will guess the User class
FactoryBot.define do
factory :user do
first_name { "John" }
last_name { "Doe" }
admin { false }
end
end
It is also possible to explicitly specify the class:
# This will use the User class (otherwise Admin would have been guessed)
factory :admin, class: "User"
You can pass a constant as well, if the constant is available (note that this can cause test performance problems in large Rails applications, since referring to the constant will cause it to be eagerly loaded).
factory :access_token, class: User
Because of the block syntax in Ruby, defining attributes as Hash
es (for
serialized/JSON columns, for example) requires two sets of curly brackets:
factory :program do
configuration { { auto_resolve: false, auto_define: true } }
end
It is recommended that you have one factory for each class that provides the simplest set of attributes necessary to create an instance of that class. If you're creating ActiveRecord objects, that means that you should only provide attributes that are required through validations and that do not have defaults. Other factories can be created through inheritance to cover common scenarios for each class.
Attempting to define multiple factories with the same name will raise an error.
Factories can be defined anywhere, but will be automatically loaded after
calling FactoryBot.find_definitions
if factories are defined in files at the
following locations:
test/factories.rb
spec/factories.rb
test/factories/*.rb
spec/factories/*.rb
Static attributes (without a block) are no longer available in factory_bot 5. You can read more about the decision to remove them in this blog post.
factory_bot supports several different build strategies: build, create, attributes_for and build_stubbed:
# Returns a User instance that's not saved
user = build(:user)
# Returns a saved User instance
user = create(:user)
# Returns a hash of attributes that can be used to build a User instance
attrs = attributes_for(:user)
# Returns an object with all defined attributes stubbed out
stub = build_stubbed(:user)
# Passing a block to any of the methods above will yield the return object
create(:user) do |user|
user.posts.create(attributes_for(:post))
end
No matter which strategy is used, it's possible to override the defined attributes by passing a hash:
# Build a User instance and override the first_name property
user = build(:user, first_name: "Joe")
user.first_name
# => "Joe"
Note that objects created with build_stubbed
cannot be serialized with
Marshal.dump
, since factory_bot defines singleton methods on these objects.
factory_bot allows you to define aliases to existing factories to make them easier to re-use. This could come in handy when, for example, your Post object has an author attribute that actually refers to an instance of a User class. While normally factory_bot can infer the factory name from the association name, in this case it will look for an author factory in vain. So, alias your user factory so it can be used under alias names.
factory :user, aliases: [:author, :commenter] do
first_name { "John" }
last_name { "Doe" }
date_of_birth { 18.years.ago }
end
factory :post do
# The alias allows us to write author instead of
# association :author, factory: :user
author
title { "How to read a book effectively" }
body { "There are five steps involved." }
end
factory :comment do
# The alias allows us to write commenter instead of
# association :commenter, factory: :user
commenter
body { "Great article!" }
end
Attributes can be based on the values of other attributes using the evaluator that is yielded to dynamic attribute blocks:
factory :user do
first_name { "Joe" }
last_name { "Blow" }
email { "#{first_name}.#{last_name}@example.com".downcase }
end
create(:user, last_name: "Doe").email
# => "joe.doe@example.com"
Transient attributes are attributes only available within the factory definition, and not set on the object being built. This allows for more complex logic inside factories.
There may be times where your code can be DRYed up by passing in transient attributes to factories. You can access transient attributes within other attributes (see Dependent Attributes):
factory :user do
transient do
rockstar { true }
end
name { "John Doe#{" - Rockstar" if rockstar}" }
end
create(:user).name
#=> "John Doe - ROCKSTAR"
create(:user, rockstar: false).name
#=> "John Doe"
Transient attributes will be ignored within attributes_for and won't be set on the model, even if the attribute exists or you attempt to override it.
If you need to access the evaluator in a factory_bot callback, you'll need to declare a second block argument (for the evaluator) and access transient attributes from there.
factory :user do
transient do
upcased { false }
end
name { "John Doe" }
after(:create) do |user, evaluator|
user.name.upcase! if evaluator.upcased
end
end
create(:user).name
#=> "John Doe"
create(:user, upcased: true).name
#=> "JOHN DOE"
Transient associations are not supported in factory_bot. Associations within the transient block will be treated as regular, non-transient associations.
If needed, you can generally work around this by building a factory within a transient attribute:
factory :post
factory :user do
transient do
post { build(:post) }
end
end
If your attributes conflict with existing methods or reserved words (all methods in the DefinitionProxy class) you can define them with add_attribute
.
factory :dna do
add_attribute(:sequence) { 'GATTACA' }
end
factory :payment do
add_attribute(:method) { 'paypal' }
end
You can easily create multiple factories for the same class without repeating common attributes by nesting factories:
factory :post do
title { "A title" }
factory :approved_post do
approved { true }
end
end
approved_post = create(:approved_post)
approved_post.title # => "A title"
approved_post.approved # => true
You can also assign the parent explicitly:
factory :post do
title { "A title" }
end
factory :approved_post, parent: :post do
approved { true }
end
As mentioned above, it's good practice to define a basic factory for each class with only the attributes required to create it. Then, create more specific factories that inherit from this basic parent. Factory definitions are still code, so keep them DRY.
It's possible to set up associations within factories. If the factory name is the same as the association name, the factory name can be left out.
factory :post do
# ...
author
end
You can define associations explicitly. This can be handy especially when Overriding attributes
factory :post do
# ...
association :author
end
You can also define associations inline within regular attributes,
but note that the value will be nil
when using the attributes_for
strategy.
factory :post do
# ...
author { association :author }
end
You can specify a different factory (although Aliases might also help you out here).
Implicitly:
factory :post do
# ...
author factory: :user
end
Explicitly:
factory :post do
# ...
association :author, factory: :user
end
Inline:
factory :post do
# ...
author { association :user }
end
You can also override attributes.
Implicitly:
factory :post do
# ...
author factory: :author, last_name: "Writely"
end
Explicitly:
factory :post do
# ...
association :author, last_name: "Writely"
end
Or inline using attributes from the factory:
factory :post do
# ...
author_last_name { "Writely" }
author { association :author, last_name: author_last_name }
end
Attribute overrides can be used to link associated objects:
FactoryBot.define do
factory :author do
name { 'Taylor' }
end
factory :post do
author
end
end
eunji = build(:author, name: 'Eunji')
post = build(:post, author: eunji)
In factory_bot 5, associations default to using the same build strategy as their parent object:
FactoryBot.define do
factory :author
factory :post do
author
end
end
post = build(:post)
post.new_record? # => true
post.author.new_record? # => true
post = create(:post)
post.new_record? # => false
post.author.new_record? # => false
This is different than the default behavior for previous versions of
factory_bot, where the association strategy would not always match the strategy
of the parent object. If you want to continue using the old behavior, you can
set the use_parent_strategy
configuration option to false
.
FactoryBot.use_parent_strategy = false
# Builds and saves a User and a Post
post = create(:post)
post.new_record? # => false
post.author.new_record? # => false
# Builds and saves a User, and then builds but does not save a Post
post = build(:post)
post.new_record? # => true
post.author.new_record? # => false
To not save the associated object, specify strategy: :build
in the factory:
FactoryBot.use_parent_strategy = false
factory :post do
# ...
association :author, factory: :user, strategy: :build
end
# Builds a User, and then builds a Post, but does not save either
post = build(:post)
post.new_record? # => true
post.author.new_record? # => true
Please note that the strategy: :build
option must be passed to an explicit call to association
,
and cannot be used with implicit associations:
factory :post do
# ...
author strategy: :build # <<< this does *not* work; causes author_id to be nil
There are a few ways to generate data for a has_many
relationship. The
simplest approach is to write a helper method in plain Ruby to tie together the
different records:
FactoryBot.define do
factory :post do
title { "Through the Looking Glass" }
user
end
factory :user do
name { "Rachel Sanchez" }
end
end
def user_with_posts(posts_count: 5)
FactoryBot.create(:user) do |user|
FactoryBot.create_list(:post, posts_count, user: user)
end
end
create(:user).posts.length # 0
user_with_posts.posts.length # 5
user_with_posts(posts_count: 15).posts.length # 15
If you prefer to keep the object creation fully within factory_bot, you can
build the posts in an after(:create)
callback.
FactoryBot.define do
factory :post do
title { "Through the Looking Glass" }
user
end
factory :user do
name { "John Doe" }
# user_with_posts will create post data after the user has been created
factory :user_with_posts do
# posts_count is declared as a transient attribute available in the
# callback via the evaluator
transient do
posts_count { 5 }
end
# the after(:create) yields two values; the user instance itself and the
# evaluator, which stores all values from the factory, including transient
# attributes; `create_list`'s second argument is the number of records
# to create and we make sure the user is associated properly to the post
after(:create) do |user, evaluator|
create_list(:post, evaluator.posts_count, user: user)
# You may need to reload the record here, depending on your application
user.reload
end
end
end
end
create(:user).posts.length # 0
create(:user_with_posts).posts.length # 5
create(:user_with_posts, posts_count: 15).posts.length # 15
Or, for a solution that works with build
, build_stubbed
, and create
(although it doesn't work well with attributes_for
), you can use inline
associations:
FactoryBot.define do
factory :post do
title { "Through the Looking Glass" }
user
end
factory :user do
name { "Taylor Kim" }
factory :user_with_posts do
posts { [association(:post)] }
end
end
end
create(:user).posts.length # 0
create(:user_with_posts).posts.length # 1
build(:user_with_posts).posts.length # 1
build_stubbed(:user_with_posts).posts.length # 1
For more flexibility you can combine this with the posts_count
transient
attribute from the callback example:
FactoryBot.define do
factory :post do
title { "Through the Looking Glass" }
user
end
factory :user do
name { "Adiza Kumato" }
factory :user_with_posts do
transient do
posts_count { 5 }
end
posts do
Array.new(posts_count) { association(:post) }
end
end
end
end
create(:user_with_posts).posts.length # 5
create(:user_with_posts, posts_count: 15).posts.length # 15
build(:user_with_posts, posts_count: 15).posts.length # 15
build_stubbed(:user_with_posts, posts_count: 15).posts.length # 15
Generating data for a has_and_belongs_to_many
relationship is very similar
to the above has_many
relationship, with a small change: you need to pass an
array of objects to the model's pluralized attribute name rather than a single
object to the singular version of the attribute name.
def profile_with_languages(languages_count: 2)
FactoryBot.create(:profile) do |profile|
FactoryBot.create_list(:language, languages_count, profiles: [profile])
end
end
Or with the callback approach:
factory :profile_with_languages do
transient do
languages_count { 2 }
end
after(:create) do |profile, evaluator|
create_list(:language, evaluator.languages_count, profiles: [profile])
profile.reload
end
end
Or the inline association approach (note the use of the instance
method here
to refer to the profile being built):
factory :profile_with_languages do
transient do
languages_count { 2 }
end
languages do
Array.new(languages_count) do
association(:language, profiles: [instance])
end
end
end
Polymorphic associations can be handled with traits:
FactoryBot.define do
factory :video
factory :photo
factory :comment do
for_photo # default to the :for_photo trait if none is specified
trait :for_video do
association :commentable, factory: :video
end
trait :for_photo do
association :commentable, factory: :photo
end
end
end
This allows us to do:
create(:comment)
create(:comment, :for_video)
create(:comment, :for_photo)
There are limitless ways objects might be interconnected, and factory_bot may not always be suited to handle those relationships. In some cases it makes sense to use factory_bot to build each individual object, and then to write helper methods in plain Ruby to tie those objects together.
That said, some more complex, interconnected relationships can be built in factory_bot
using inline associations with reference to the instance
being built.
Let's say your models look like this, where an associated Student
and
Profile
should both belong to the same School
:
class Student < ApplicationRecord
belongs_to :school
has_one :profile
end
class Profile < ApplicationRecord
belongs_to :school
belongs_to :student
end
class School < ApplicationRecord
has_many :students
has_many :profiles
end
We can ensure the student and profile are connected to each other and to the same school with a factory like this:
FactoryBot.define do
factory :student do
school
profile { association :profile, student: instance, school: school }
end
factory :profile do
school
student { association :student, profile: instance, school: school }
end
factory :school
end
Note that this approach works with build
, build_stubbed
, and create
, but
the associations will return nil
when using attributes_for
.
Also, note that if you assign any attributes inside a custom initialize_with
(e.g. initialize_with { new(**attributes) }
), those attributes should not refer to instance
,
since it will be nil
.
Unique values in a specific format (for example, e-mail addresses) can be
generated using sequences. Sequences are defined by calling sequence
in a
definition block, and values in a sequence are generated by calling
generate
:
# Defines a new sequence
FactoryBot.define do
sequence :email do |n|
"person#{n}@example.com"
end
end
generate :email
# => "person1@example.com"
generate :email
# => "person2@example.com"
Sequences can be used in dynamic attributes:
factory :invite do
invitee { generate(:email) }
end
Or as implicit attributes:
factory :user do
email # Same as `email { generate(:email) }`
end
Note that defining sequences as implicit attributes will not work if you have a factory with the same name as the sequence.
And it's also possible to define an in-line sequence that is only used in a particular factory:
factory :user do
sequence(:email) { |n| "person#{n}@example.com" }
end
You can override the initial value. Any value that responds to the #next
method will work (e.g. 1, 2, 3, 'a', 'b', 'c')
factory :user do
sequence(:email, 1000) { |n| "person#{n}@example.com" }
end
Without a block, the value will increment itself, starting at its initial value:
factory :post do
sequence(:position)
end
Please note, that the value for the sequence could be any Enumerable instance,
as long as it responds to #next
:
factory :task do
sequence :priority, %i[low medium high urgent].cycle
end
Sequences can also have aliases. The sequence aliases share the same counter:
factory :user do
sequence(:email, 1000, aliases: [:sender, :receiver]) { |n| "person#{n}@example.com" }
end
# will increase value counter for :email which is shared by :sender and :receiver
generate(:sender)
Define aliases and use default value (1) for the counter
factory :user do
sequence(:email, aliases: [:sender, :receiver]) { |n| "person#{n}@example.com" }
end
Setting the value:
factory :user do
sequence(:email, 'a', aliases: [:sender, :receiver]) { |n| "person#{n}@example.com" }
end
The value just needs to support the #next
method. Here the next value will be 'a', then 'b', etc.
Sequences can also be rewound with FactoryBot.rewind_sequences
:
sequence(:email) {|n| "person#{n}@example.com" }
generate(:email) # "person1@example.com"
generate(:email) # "person2@example.com"
generate(:email) # "person3@example.com"
FactoryBot.rewind_sequences
generate(:email) # "person1@example.com"
This rewinds all registered sequences.
When working with uniqueness constraints, be careful not to pass in override values that will conflict with the generated sequence values.
In this example the email will be the same for both users. If email must be unique, this code will error:
factory :user do
sequence(:email) { |n| "person#{n}@example.com" }
end
FactoryBot.create(:user, email: "person1@example.com")
FactoryBot.create(:user)
Traits allow you to group attributes together and then apply them to any factory.
factory :user, aliases: [:author]
factory :story do
title { "My awesome story" }
author
trait :published do
published { true }
end
trait :unpublished do
published { false }
end
trait :week_long_publishing do
start_at { 1.week.ago }
end_at { Time.now }
end
trait :month_long_publishing do
start_at { 1.month.ago }
end_at { Time.now }
end
factory :week_long_published_story, traits: [:published, :week_long_publishing]
factory :month_long_published_story, traits: [:published, :month_long_publishing]
factory :week_long_unpublished_story, traits: [:unpublished, :week_long_publishing]
factory :month_long_unpublished_story, traits: [:unpublished, :month_long_publishing]
end
Traits can be used as implicit attributes:
factory :week_long_published_story_with_title, parent: :story do
published
week_long_publishing
title { "Publishing that was started at #{start_at}" }
end
Note that defining traits as implicit attributes will not work if you have a factory or sequence with the same name as the trait.
Traits that define the same attributes won't raise AttributeDefinitionErrors; the trait that defines the attribute latest gets precedence.
factory :user do
name { "Friendly User" }
login { name }
trait :active do
name { "John Doe" }
status { :active }
login { "#{name} (active)" }
end
trait :inactive do
name { "Jane Doe" }
status { :inactive }
login { "#{name} (inactive)" }
end
trait :admin do
admin { true }
login { "admin-#{name}" }
end
factory :active_admin, traits: [:active, :admin] # login will be "admin-John Doe"
factory :inactive_admin, traits: [:admin, :inactive] # login will be "Jane Doe (inactive)"
end
You can override individual attributes granted by a trait in a child factory:
factory :user do
name { "Friendly User" }
login { name }
trait :active do
name { "John Doe" }
status { :active }
login { "#{name} (M)" }
end
factory :brandon do
active
name { "Brandon" }
end
end
Traits can be defined outside of factories and used as mixins to compose shared attributes
FactoryBot.define do
trait :timestamps do
created_at { 8.days.ago }
updated_at { 4.days.ago }
end
factory :user, traits: [:timestamps] do
username { "john_doe" }
end
factory :post do
timestamps
title { "Traits rock" }
end
end
Traits can also be passed in as a list of symbols when you construct an instance from factory_bot.
factory :user do
name { "Friendly User" }
trait :active do
name { "John Doe" }
status { :active }
end
trait :admin do
admin { true }
end
end
# creates an admin user with :active status and name "Jon Snow"
create(:user, :admin, :active, name: "Jon Snow")
This ability works with build
, build_stubbed
, attributes_for
, and create
.
create_list
and build_list
methods are supported as well. Just remember to pass
the number of instances to create/build as second parameter, as documented in the
"Building or Creating Multiple Records" section of this file.
factory :user do
name { "Friendly User" }
trait :admin do
admin { true }
end
end
# creates 3 admin users with :active status and name "Jon Snow"
create_list(:user, 3, :admin, :active, name: "Jon Snow")
Traits can be used with associations easily too:
factory :user do
name { "Friendly User" }
trait :admin do
admin { true }
end
end
factory :post do
association :user, :admin, name: 'John Doe'
end
# creates an admin user with name "John Doe"
create(:post).user
When you're using association names that're different than the factory:
factory :user do
name { "Friendly User" }
trait :admin do
admin { true }
end
end
factory :post do
association :author, :admin, factory: :user, name: 'John Doe'
# or
association :author, factory: [:user, :admin], name: 'John Doe'
end
# creates an admin user with name "John Doe"
create(:post).author
Traits can be used within other traits to mix in their attributes.
factory :order do
trait :completed do
completed_at { 3.days.ago }
end
trait :refunded do
completed
refunded_at { 1.day.ago }
end
end
Finally, traits can accept transient attributes.
factory :invoice do
trait :with_amount do
transient do
amount { 1 }
end
after(:create) do |invoice, evaluator|
create :line_item, invoice: invoice, amount: evaluator.amount
end
end
end
create :invoice, :with_amount, amount: 2
Given an Active Record model with an enum attribute:
class Task < ActiveRecord::Base
enum status: {queued: 0, started: 1, finished: 2}
end
factory_bot will automatically define traits for each possible value of the enum:
FactoryBot.define do
factory :task
end
FactoryBot.build(:task, :queued)
FactoryBot.build(:task, :started)
FactoryBot.build(:task, :finished)
Writing the traits out manually would be cumbersome, and is not necessary:
FactoryBot.define do
factory :task do
trait :queued do
status { :queued }
end
trait :started do
status { :started }
end
trait :finished do
status { :finished }
end
end
end
If automatically defining traits for enum attributes on every factory is not
desired, it is possible to disable the feature by setting
FactoryBot.automatically_define_enum_traits = false
In that case, it is still possible to explicitly define traits for an enum attribute in a particular factory:
FactoryBot.automatically_define_enum_traits = false
FactoryBot.define do
factory :task do
traits_for_enum(:status)
end
end
It is also possible to use this feature for other enumerable values, not specifically tied to Active Record enum attributes.
With an array:
class Task
attr_accessor :status
end
FactoryBot.define do
factory :task do
traits_for_enum(:status, ["queued", "started", "finished"])
end
end
Or with a hash:
class Task
attr_accessor :status
end
FactoryBot.define do
factory :task do
traits_for_enum(:status, { queued: 0, started: 1, finished: 2 })
end
end
factory_bot makes available four callbacks for injecting some code:
- after(:build) - called after a factory is built (via
FactoryBot.build
,FactoryBot.create
) - before(:create) - called before a factory is saved (via
FactoryBot.create
) - after(:create) - called after a factory is saved (via
FactoryBot.create
) - after(:stub) - called after a factory is stubbed (via
FactoryBot.build_stubbed
)
Examples:
# Define a factory that calls the generate_hashed_password method after it is built
factory :user do
after(:build) { |user| generate_hashed_password(user) }
end
Note that you'll have an instance of the user in the block. This can be useful.
You can also define multiple types of callbacks on the same factory:
factory :user do
after(:build) { |user| do_something_to(user) }
after(:create) { |user| do_something_else_to(user) }
end
Factories can also define any number of the same kind of callback. These callbacks will be executed in the order they are specified:
factory :user do
after(:create) { this_runs_first }
after(:create) { then_this }
end
Calling create
will invoke both after_build
and after_create
callbacks.
Also, like standard attributes, child factories will inherit (and can also define) callbacks from their parent factory.
Multiple callbacks can be assigned to run a block; this is useful when building various strategies that run the same code (since there are no callbacks that are shared across all strategies).
factory :user do
callback(:after_stub, :before_create) { do_something }
after(:stub, :create) { do_something_else }
before(:create, :custom) { do_a_third_thing }
end
To override callbacks for all factories, define them within the
FactoryBot.define
block:
FactoryBot.define do
after(:build) { |object| puts "Built #{object}" }
after(:create) { |object| AuditLog.create(attrs: object.attributes) }
factory :user do
name { "John Doe" }
end
end
You can call callbacks that rely on Symbol#to_proc
:
# app/models/user.rb
class User < ActiveRecord::Base
def confirm!
# confirm the user account
end
end
# spec/factories.rb
FactoryBot.define do
factory :user do
after :create, &:confirm!
end
end
create(:user) # creates the user and confirms it
If you're given a set of factories (say, from a gem developer) but want to change them to fit into your application better, you can modify that factory instead of creating a child factory and adding attributes there.
If a gem were to give you a User factory:
FactoryBot.define do
factory :user do
full_name { "John Doe" }
sequence(:username) { |n| "user#{n}" }
password { "password" }
end
end
Instead of creating a child factory that added additional attributes:
FactoryBot.define do
factory :application_user, parent: :user do
full_name { "Jane Doe" }
date_of_birth { 21.years.ago }
health { 90 }
end
end
You could modify that factory instead.
FactoryBot.modify do
factory :user do
full_name { "Jane Doe" }
date_of_birth { 21.years.ago }
health { 90 }
end
end
When modifying a factory, you can change any of the attributes you want (aside from callbacks).
FactoryBot.modify
must be called outside of a FactoryBot.define
block as it operates on factories differently.
A caveat: you can only modify factories (not sequences or traits) and callbacks still compound as they normally would. So, if
the factory you're modifying defines an after(:create)
callback, you defining an after(:create)
won't override it, it'll just get run after the first callback.
Sometimes, you'll want to create or build multiple instances of a factory at once.
built_users = build_list(:user, 25)
created_users = create_list(:user, 25)
These methods will build or create a specific amount of factories and return them as an array. To set the attributes for each of the factories, you can pass in a hash as you normally would.
twenty_year_olds = build_list(:user, 25, date_of_birth: 20.years.ago)
In order to set different attributes for each factory, these methods may be passed a block, with the factory and the index as parameters:
twenty_somethings = build_list(:user, 10) do |user, i|
user.date_of_birth = (20 + i).years.ago
end
create_list
passes saved instances into the block. If you modify the instance, you must save it again:
twenty_somethings = create_list(:user, 10) do |user, i|
user.date_of_birth = (20 + i).years.ago
user.save!
end
build_stubbed_list
will give you fully stubbed out instances:
stubbed_users = build_stubbed_list(:user, 25) # array of stubbed users
There's also a set of *_pair
methods for creating two records at a time:
built_users = build_pair(:user) # array of two built users
created_users = create_pair(:user) # array of two created users
If you need multiple attribute hashes, attributes_for_list
will generate them:
users_attrs = attributes_for_list(:user, 25) # array of attribute hashes
factory_bot allows for linting known factories:
FactoryBot.lint
FactoryBot.lint
creates each factory and catches any exceptions raised
during the creation process. FactoryBot::InvalidFactoryError
is raised with
a list of factories (and corresponding exceptions) for factories which could
not be created.
Recommended usage of FactoryBot.lint
is to run this in a task
before your test suite is executed.
Running it in a before(:suite)
,
will negatively impact the performance
of your tests
when running single tests.
Example Rake task:
# lib/tasks/factory_bot.rake
namespace :factory_bot do
desc "Verify that all FactoryBot factories are valid"
task lint: :environment do
if Rails.env.test?
conn = ActiveRecord::Base.connection
conn.transaction do
FactoryBot.lint
raise ActiveRecord::Rollback
end
else
system("bundle exec rake factory_bot:lint RAILS_ENV='test'")
fail if $?.exitstatus.nonzero?
end
end
end
After calling FactoryBot.lint
, you'll likely want to clear out the
database, as records will most likely be created. The provided example above
uses an sql transaction and rollback to leave the database clean.
You can lint factories selectively by passing only factories you want linted:
factories_to_lint = FactoryBot.factories.reject do |factory|
factory.name =~ /^old_/
end
FactoryBot.lint factories_to_lint
This would lint all factories that aren't prefixed with old_
.
Traits can also be linted. This option verifies that each
and every trait of a factory generates a valid object on its own.
This is turned on by passing traits: true
to the lint
method:
FactoryBot.lint traits: true
This can also be combined with other arguments:
FactoryBot.lint factories_to_lint, traits: true
You can also specify the strategy used for linting:
FactoryBot.lint strategy: :build
Verbose linting will include full backtraces for each error, which can be helpful for debugging:
FactoryBot.lint verbose: true
If you want to use factory_bot to construct an object where some attributes
are passed to initialize
or if you want to do something other than simply
calling new
on your build class, you can override the default behavior by
defining initialize_with
on your factory. Example:
# user.rb
class User
attr_accessor :name, :email
def initialize(name)
@name = name
end
end
# factories.rb
sequence(:email) { |n| "person#{n}@example.com" }
factory :user do
name { "Jane Doe" }
email
initialize_with { new(name) }
end
build(:user).name # Jane Doe
Although factory_bot is written to work with ActiveRecord out of the box, it
can also work with any Ruby class. For maximum compatibility with ActiveRecord,
the default initializer builds all instances by calling new
on your build class
without any arguments. It then calls attribute writer methods to assign all the
attribute values. While that works fine for ActiveRecord, it actually doesn't
work for almost any other Ruby class.
You can override the initializer in order to:
- Build non-ActiveRecord objects that require arguments to
initialize
- Use a method other than
new
to instantiate the instance - Do wild things like decorate the instance after it's built
When using initialize_with
, you don't have to declare the class itself when
calling new
; however, any other class methods you want to call will have to
be called on the class explicitly.
For example:
factory :user do
name { "John Doe" }
initialize_with { User.build_with_name(name) }
end
You can also access all public attributes within the initialize_with
block
by calling attributes
:
factory :user do
transient do
comments_count { 5 }
end
name "John Doe"
initialize_with { new(**attributes) }
end
This will build a hash of all attributes to be passed to new
. It won't
include transient attributes, but everything else defined in the factory will be
passed (associations, evaluated sequences, etc.)
You can define initialize_with
for all factories by including it in the
FactoryBot.define
block:
FactoryBot.define do
initialize_with { new("Awesome first argument") }
end
When using initialize_with
, attributes accessed from within the initialize_with
block are assigned only in the constructor; this equates to roughly the
following code:
FactoryBot.define do
factory :user do
initialize_with { new(name) }
name { 'value' }
end
end
build(:user)
# runs
User.new('value')
This prevents duplicate assignment; in versions of factory_bot before 4.0, it would run this:
FactoryBot.define do
factory :user do
initialize_with { new(name) }
name { 'value' }
end
end
build(:user)
# runs
user = User.new('value')
user.name = 'value'
There are times where you may want to extend behavior of factory_bot by adding a custom build strategy.
Strategies define two methods: association
and result
. association
receives a FactoryBot::FactoryRunner
instance, upon which you can call
run
, overriding the strategy if you want. The second method, result
,
receives a FactoryBot::Evaluation
instance. It provides a way to trigger
callbacks (with notify
), object
or hash
(to get the result instance or a
hash based on the attributes defined in the factory), and create
, which
executes the to_create
callback defined on the factory.
To understand how factory_bot uses strategies internally, it's probably easiest to just view the source for each of the four default strategies.
Here's an example of composing a strategy using
FactoryBot::Strategy::Create
to build a JSON representation of your model.
class JsonStrategy
def initialize
@strategy = FactoryBot.strategy_by_name(:create).new
end
delegate :association, to: :@strategy
def result(evaluation)
@strategy.result(evaluation).to_json
end
def to_sym
:json
end
end
For factory_bot to recognize the new strategy, you can register it:
FactoryBot.register_strategy(:json, JsonStrategy)
This allows you to call
FactoryBot.json(:user)
Finally, you can override factory_bot's own strategies if you'd like by registering a new object in place of the strategies.
Custom callbacks can be defined if you're using custom strategies:
class JsonStrategy
def initialize
@strategy = FactoryBot.strategy_by_name(:create).new
end
delegate :association, to: :@strategy
def result(evaluation)
result = @strategy.result(evaluation)
evaluation.notify(:before_json, result)
result.to_json.tap do |json|
evaluation.notify(:after_json, json)
evaluation.notify(:make_json_awesome, json)
end
end
def to_sym
:json
end
end
FactoryBot.register_strategy(:json, JsonStrategy)
FactoryBot.define do
factory :user do
before(:json) { |user| do_something_to(user) }
after(:json) { |user_json| do_something_to(user_json) }
callback(:make_json_awesome) { |user_json| do_something_to(user_json) }
end
end
By default, creating a record will call save!
on the instance; since this
may not always be ideal, you can override that behavior by defining
to_create
on the factory:
factory :different_orm_model do
to_create { |instance| instance.persist! }
end
To disable the persistence method altogether on create, you can skip_create
for that factory:
factory :user_without_database do
skip_create
end
To override to_create
for all factories, define it within the
FactoryBot.define
block:
FactoryBot.define do
to_create { |instance| instance.persist! }
factory :user do
name { "John Doe" }
end
end
In order to track what factories are created (and with what build strategy),
ActiveSupport::Notifications
are included to provide a way to subscribe to
factories being run. One example would be to track factories based on a
threshold of execution time.
ActiveSupport::Notifications.subscribe("factory_bot.run_factory") do |name, start, finish, id, payload|
execution_time_in_seconds = finish - start
if execution_time_in_seconds >= 0.5
$stderr.puts "Slow factory: #{payload[:name]} using strategy #{payload[:strategy]}"
end
end
Another example would be tracking all factories and how they're used
throughout your test suite. If you're using RSpec, it's as simple as adding a
before(:suite)
and after(:suite)
:
factory_bot_results = {}
config.before(:suite) do
ActiveSupport::Notifications.subscribe("factory_bot.run_factory") do |name, start, finish, id, payload|
factory_name = payload[:name]
strategy_name = payload[:strategy]
factory_bot_results[factory_name] ||= {}
factory_bot_results[factory_name][strategy_name] ||= 0
factory_bot_results[factory_name][strategy_name] += 1
end
end
config.after(:suite) do
puts factory_bot_results
end
When running RSpec with a Rails preloader such as spring
or zeus
, it's possible
to encounter an ActiveRecord::AssociationTypeMismatch
error when creating a factory
with associations, as below:
FactoryBot.define do
factory :united_states, class: "Location" do
name { 'United States' }
association :location_group, factory: :north_america
end
factory :north_america, class: "LocationGroup" do
name { 'North America' }
end
end
The error occurs during the run of the test suite:
Failure/Error: united_states = create(:united_states)
ActiveRecord::AssociationTypeMismatch:
LocationGroup(#70251250797320) expected, got LocationGroup(#70251200725840)
The two possible solutions are to either run the suite without the preloader, or
to add FactoryBot.reload
to the RSpec configuration, like so:
RSpec.configure do |config|
config.before(:suite) { FactoryBot.reload }
end
If you're not using Bundler, be sure to have the gem installed and call:
require 'factory_bot'
Once required, assuming you have a directory structure of spec/factories
or
test/factories
, all you'll need to do is run:
FactoryBot.find_definitions
If you're using a separate directory structure for your factories, you can change the definition file paths before trying to find definitions:
FactoryBot.definition_file_paths = %w(custom_factories_directory)
FactoryBot.find_definitions
If you don't have a separate directory of factories and would like to define them inline, that's possible as well:
require 'factory_bot'
FactoryBot.define do
factory :user do
name { 'John Doe' }
date_of_birth { 21.years.ago }
end
end