thoughtbot--shoulda-matchers/README.md

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

📖 Read the documentation for the latest version (4.1.2).
📢 See what's changed in a recent version.

Table of contents

• Getting started
  • RSpec
  • Minitest
• Usage
  • On the subject of subject
  • Availability of RSpec matchers in example groups
  • should vs is_expected.to
• Matchers
  • ActiveModel matchers
  • ActiveRecord matchers
  • ActionController matchers
  • Independent matchers
• Compatibility
• Contributing
• Versioning
• License
• About thoughtbot

Getting started

RSpec

Start by including shoulda-matchers in your Gemfile:

group :test do
  gem 'shoulda-matchers'
end

Now you need to tell the gem a couple of things:

• Which test framework you're using
• Which portion of the matchers you want to use

You can supply this information by providing a configuration block. Where this goes and what this contains depends on your project.

Rails apps

Assuming you are testing 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

Now you're ready to use matchers in your tests!

Non-Rails apps

If your project isn't a Rails app, but you still make use of ActiveRecord or ActiveModel, 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

Now you're ready to use matchers in your tests!

Minitest

Shoulda Matchers was originally a component of Shoulda, a gem that also provides should and context syntax via shoulda-context.

At the moment, shoulda has not been updated to support shoulda-matchers 3.x and 4.x, so you'll want to add the following to your Gemfile:

group :test do
  gem 'shoulda', '~> 3.5'
  gem 'shoulda-matchers', '~> 2.0'
  gem 'rails-controller-testing'
end

Now you're ready to use matchers in your tests!

Usage

The matchers provided by this gem are divided into different categories depending on what you're testing within your Rails app:

• database models backed by ActiveRecord
• non-database models, form objects, etc. backed by ActiveModel
• controllers
• routes (RSpec only)
• usage of Rails-specific features like delegate

All matchers are designed to be prepended primarily with the word should, which is a special directive 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

For the full set of matchers you can use, see below.

On the subject of subject

For both RSpec and Shoulda, the subject is an implicit reference to the object under test, and all of the matchers make use of it internally when they are run. This is always set automatically by your test framework in any given test case; however, in certain cases it can be advantageous to override the subject. 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

If you're using RSpec, then you're probably familiar with the concept of example groups: these are different kinds of test cases, and each of them has special behavior around them. As alluded to above, this gem works in a similar way, and there are matchers that are only available in certain types of example groups:

• ActiveRecord and ActiveModel matchers are available only in model example groups, i.e., those tagged with type: :model or in files located under spec/models.
• ActionController matchers are available only in controller example groups, i.e., those tagged with type: :controller or in files located under spec/controllers.
• The route matcher is available in routing example groups, i.e., those tagged with type: :routing or in files located under spec/routing.
• Independent matchers are available in all example groups.

As long as you're using Rails, you don't need to worry about this — everything should "just work".

However, if you are using ActiveModel or ActiveRecord outside of Rails, and you want to use model matchers in certain example groups, you'll need to manually include the module that holds those matchers. A good way to do this is to place the following in your spec_helper.rb:

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

Then you can say:

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

should vs is_expected.to

In this README and throughout the documentation, we're using the should form of RSpec's one-liner syntax over is_expected.to. The should form works regardless of how you've configured RSpec — meaning you can still use it even when using the expect syntax. 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

Matchers

The following is a list of matchers shipped with the gem. If you need details about any of them, make sure to consult the documentation!

ActiveModel matchers

• allow_value tests that an attribute is valid or invalid if set to one or more values. (Aliased as #allow_values.)
• have_secure_password tests usage of has_secure_password.
• validate_absence_of tests usage of validates_absence_of.
• validate_acceptance_of tests usage of validates_acceptance_of.
• validate_confirmation_of tests usage of validates_confirmation_of.
• validate_exclusion_of tests usage of validates_exclusion_of.
• validate_inclusion_of tests usage of validates_inclusion_of.
• validate_length_of tests usage of validates_length_of.
• validate_numericality_of tests usage of validates_numericality_of.
• validate_presence_of tests usage of validates_presence_of.

ActiveRecord matchers

• accept_nested_attributes_for tests usage of the accepts_nested_attributes_for macro.
• belong_to tests your belongs_to associations.
• define_enum_for tests usage of the enum macro.
• have_and_belong_to_many tests your has_and_belongs_to_many associations.
• have_db_column tests that the table that backs your model has a specific column.
• have_db_index tests that the table that backs your model has an index on a specific column.
• have_many tests your has_many associations.
• have_one tests your has_one associations.
• have_readonly_attribute tests usage of the attr_readonly macro.
• serialize tests usage of the serialize macro.
• validate_uniqueness_of tests usage of validates_uniqueness_of.

ActionController matchers

• filter_param tests parameter filtering configuration.
• permit tests that an action places a restriction on the params hash.
• redirect_to tests that an action redirects to a certain location.
• render_template tests that an action renders a template.
• render_with_layout tests that an action is rendered with a certain layout.
• rescue_from tests usage of the rescue_from macro.
• respond_with tests that an action responds with a certain status code.
• route tests your routes.
• set_session makes assertions on the session hash.
• set_flash makes assertions on the flash hash.
• use_after_action tests that an after_action callback is defined in your controller.
• use_around_action tests that an around_action callback is defined in your controller.
• use_before_action tests that a before_action callback is defined in your controller.

Routing matchers

• route tests your routes.

Independent matchers

• delegate_method tests that an object forwards messages to other, internal objects by way of delegation.

Compatibility

Shoulda Matchers is tested and supported against Ruby 2.4+, Rails 5.x, Rails 4.2.x, RSpec 3.x, and Minitest 5.x.

For Ruby < 2.4 and Rails < 4.1 compatibility, please use v3.1.3.

Contributing

Shoulda Matchers is open source, and we are grateful for everyone who's contributed so far.

If you'd like to contribute, please take a look at the instructions for installing dependencies and crafting a good pull request.

Versioning

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

License

Shoulda Matchers is copyright © 2006-2019 thoughtbot, inc. It is free software, and may be redistributed under the terms specified in the MIT-LICENSE file.

About thoughtbot

Shoulda Matchers is maintained and funded by thoughtbot, inc. The names and logos for thoughtbot are trademarks of thoughtbot, inc.

We are passionate about open source software. See our other projects. We are available for hire.