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shoulda-matchers

Shoulda Matchers provides RSpec- and Minitest-compatible one-liners to test common Rails functionality that, if written by hand, would be much longer, more complex, and error-prone.

Quick links

šŸ“– Read the documentation for the latest version. šŸ“¢ See what's changed in recent versions.

Table of contents

Getting started

RSpec

Start by including shoulda-matchers in your Gemfile:

group :test do
  gem 'shoulda-matchers', '~> 6.0'
end

Then run bundle install.

Now you need to configure the gem by telling it:

Rails apps

If you're working on a Rails app, simply place this at the bottom of spec/rails_helper.rb (or in a support file if you so choose):

Shoulda::Matchers.configure do |config|
  config.integrate do |with|
    with.test_framework :rspec
    with.library :rails
  end
end

Non-Rails apps

If you're not working on a Rails app, but you still make use of ActiveRecord or ActiveModel in your project, you can still use this gem too! In that case, you'll want to place the following configuration at the bottom of spec/spec_helper.rb:

Shoulda::Matchers.configure do |config|
  config.integrate do |with|
    with.test_framework :rspec

    # Keep as many of these lines as are necessary:
    with.library :active_record
    with.library :active_model
  end
end

Minitest

If you're using our umbrella gem Shoulda, then make sure that you're using the latest version:

group :test do
  gem 'shoulda', '~> 4.0'
end

Otherwise, add shoulda-matchers to your Gemfile:

group :test do
  gem 'shoulda-matchers', '~> 6.0'
end

Then run bundle install.

Now you need to configure the gem by telling it:

Rails apps

If you're working on a Rails app, simply place this at the bottom of test/test_helper.rb:

Shoulda::Matchers.configure do |config|
  config.integrate do |with|
    with.test_framework :minitest
    with.library :rails
  end
end

Non-Rails apps

If you're not working on a Rails app, but you still make use of ActiveRecord or ActiveModel in your project, you can still use this gem too! In that case, you'll want to place the following configuration at the bottom of test/test_helper.rb:

Shoulda::Matchers.configure do |config|
  config.integrate do |with|
    with.test_framework :minitest

    # Keep as many of these lines as are necessary:
    with.library :active_record
    with.library :active_model
  end
end

Usage

Most of the matchers provided by this gem are useful in a Rails context, and as such, can be used for different parts of a Rails app:

As the name of the gem indicates, most matchers are designed to be used in "one-liner" form using the should macro, a special directive available in both RSpec and Shoulda. For instance, a model test case may look something like:

# RSpec
RSpec.describe MenuItem, type: :model do
  describe 'associations' do
    it { should belong_to(:category).class_name('MenuCategory') }
  end

  describe 'validations' do
    it { should validate_presence_of(:name) }
    it { should validate_uniqueness_of(:name).scoped_to(:category_id) }
  end
end

# Minitest (Shoulda)
class MenuItemTest < ActiveSupport::TestCase
  context 'associations' do
    should belong_to(:category).class_name('MenuCategory')
  end

  context 'validations' do
    should validate_presence_of(:name)
    should validate_uniqueness_of(:name).scoped_to(:category_id)
  end
end

See below for the full set of matchers that you can use.

On the subject of subject

For both RSpec and Shoulda, the subject is an implicit reference to the object under test, and through the use of should as demonstrated above, all of the matchers make use of subject internally when they are run. A subject is always set automatically by your test framework in any given test case; however, in certain cases it can be advantageous to override it. For instance, when testing validations in a model, it is customary to provide a valid model instead of a fresh one:

# RSpec
RSpec.describe Post, type: :model do
  describe 'validations' do
    # Here we're using FactoryBot, but you could use anything
    subject { build(:post) }

    it { should validate_presence_of(:title) }
  end
end

# Minitest (Shoulda)
class PostTest < ActiveSupport::TestCase
  context 'validations' do
    subject { build(:post) }

    should validate_presence_of(:title)
  end
end

When overriding the subject in this manner, then, it's important to provide the correct object. When in doubt, provide an instance of the class under test. This is particularly necessary for controller tests, where it is easy to accidentally write something like:

RSpec.describe PostsController, type: :controller do
  describe 'GET #index' do
    subject { get :index }

    # This may work...
    it { should have_http_status(:success) }
    # ...but this will not!
    it { should permit(:title, :body).for(:post) }
  end
end

In this case, you would want to use before rather than subject:

RSpec.describe PostsController, type: :controller do
  describe 'GET #index' do
    before { get :index }

    # Notice that we have to assert have_http_status on the response here...
    it { expect(response).to have_http_status(:success) }
    # ...but we do not have to provide a subject for render_template
    it { should render_template('index') }
  end
end

Availability of RSpec matchers in example groups

Rails projects

If you're using RSpec, then you're probably familiar with the concept of example groups. Example groups can be assigned tags order to assign different behavior to different kinds of example groups. This comes into play especially when using rspec-rails, where, for instance, controller example groups, tagged with type: :controller, are written differently than request example groups, tagged with type: :request. This difference in writing style arises because rspec-rails mixes different behavior and methods into controller example groups vs. request example groups.

Relying on this behavior, Shoulda Matchers automatically makes certain matchers available in certain kinds of example groups:

As long as you're using Rails, you don't need to worry about these details ā€” everything should "just work".

Non-Rails projects

What if you are using ActiveModel or ActiveRecord outside of Rails, however, and you want to use model matchers in a certain example group? Then you'll need to manually include the module that holds those matchers into that example group. For instance, you might have to say:

RSpec.describe MySpecialModel do
  include Shoulda::Matchers::ActiveModel
  include Shoulda::Matchers::ActiveRecord
end

If you have a lot of similar example groups in which you need to do this, then you might find it more helpful to tag your example groups appropriately, then instruct RSpec to mix these modules into any example groups that have that tag. For instance, you could add this to your rails_helper.rb:

RSpec.configure do |config|
  config.include(Shoulda::Matchers::ActiveModel, type: :model)
  config.include(Shoulda::Matchers::ActiveRecord, type: :model)
end

And from then on, you could say:

RSpec.describe MySpecialModel, type: :model do
  # ...
end

should vs is_expected.to

In this README and throughout the documentation, you'll notice that we use the should form of RSpec's one-liner syntax over is_expected.to. Beside being the namesake of the gem itself, this is our preferred syntax as it's short and sweet. But if you prefer to use is_expected.to, you can do that too:

RSpec.describe Person, type: :model do
  it { is_expected.to validate_presence_of(:name) }
end

A Note on Testing Style

If you inspect the source code, you'll notice quickly that shoulda-matchers is largely implemented using reflections and other introspection methods that Rails provides. On first sight, this might seem to go against the common practice of testing behavior rather than implementation. However, as the available matchers indicate, we recommend that you treat shoulda-matchers as a tool to help you ensure correct configuration and adherence to best practices and idiomatic Rails in your models and controllers - especially for aspects that in your experience are often insufficiently tested, such as ActiveRecord validations or controller callbacks (a.k.a. the "framework-y" parts).

For testing your application's unique business logic, however, we recommend focusing on behavior and outcomes over implementation details. This approach will better support refactoring and ensure that your tests remain resilient to changes in how your code is structured. While no generalized testing tool can fully capture the nuances of your specific domain, you can draw inspiration from shoulda-matchers to write custom matchers that align more closely with your application's needs.

Matchers

Here is the full list of matchers that ship with this gem. If you need details about any of them, make sure to consult the documentation!

ActiveModel matchers

ActiveRecord matchers

ActionController matchers

Routing matchers

Independent matchers

Extensions

Over time our community has created extensions to Shoulda Matchers. If you've created something that you want to share, please let us know!

Contributing

Have a fix for a problem you've been running into or an idea for a new feature you think would be useful? Take a look at the Contributing document for instructions on setting up the repo on your machine, understanding the codebase, and creating a good pull request.

Compatibility

Shoulda Matchers is tested and supported against Ruby 3.0+, Rails 6.1+, RSpec 3.x, and Minitest 5.x.

Versioning

Shoulda Matchers follows Semantic Versioning 2.0 as defined at https://semver.org.

Team

Shoulda Matchers is currently maintained by Pedro Paiva and Matheus Sales. Previous maintainers include Elliot Winkler, Gui Albuk, Jason Draper, Melissa Xie, Gabe Berke-Williams, Ryan McGeary, Joe Ferris, and Tammer Saleh.

Copyright/License

Shoulda Matchers is copyright Ā© Tammer Saleh and thoughtbot, inc. It is free and opensource software and may be redistributed under the terms specified in the LICENSE file.

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