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Make Rails Use MiniTest::Spec!

The minitest-spec-rails gem makes it easy to use the MiniTest::Spec DSL within your existing Rails 2.3, 3.x or 4.x test suite. It does this by forcing ActiveSupport::TestCase to utilize the MiniTest::Spec::DSL.

Gem Version CI Status Maintainability


Existing or new Rails applications that use the default Rails testing structure can simply drop in the minitest-spec-gem and start writing their tests in the new spec DSL. Since MiniTest::Spec is built on top of MiniTest::Unit, a replacement for Test::Unit, all of your existing tests will continue to work.

Rails 4.1 to 6.0

Our master branch is tracking rails 5.1 up to 6.x active development.

group :test do
  gem 'minitest-spec-rails'

For Rails 3.x or 4.0

Our 3-x-stable branch is meant for both Rails 3.x or 4.0 specifically. This version uses the latest 4.x series of minitest.

group :test do
  gem 'minitest-spec-rails', '~> 4.7'

How is this different than MiniTest::Rails?

To start off both Mike Moore (@blowmage) and I have worked together and we both LOVE MiniTest::Spec. Both projects aim to advocate MiniTest and make Rails integration as easy as possible. However, there are a few key differences in our projects. Some of these differences may go away in time too. As always, choose the tool you think fits your needs. So how, is minitest-spec-rails different than minitest-rails?

  • We aim to leverage existing Rails test directories and files!
  • No special test helper and/or generators.
  • Easy migration path for existing Rails applications.
  • How we go about freedom patching Rails.
  • Fully support Ruby 1.8.7 with all legacy Test::Unit behavior.
  • Compatibility with ActiveSupport::TestCase's setup and teardowns.

So the goal of this project is to make Rails 3 or 4 applications just work as if rails-core had decided to support MiniTest::Spec all along. We believe that eventually that day will come and when it does, all your tests will still work! So bundle up and get started!

gem 'minitest-spec-rails'

Test Styles

This cheat sheet shows both the MiniTest::Unit assertions along with the MiniTest::Spec assertion syntax. Remember, MiniTest::Spec is built on top of MiniTest::Unit which is a Test::Unit replacement. That means you can mix and match styles as you upgrade from Test::Unit to a more modern style. For example, both of these would work in MiniTest::Spec and are interchangeable.

# MiniTest::Unit Assertion Style:
assert_equal 100, foo

# MiniTest::Spec Assertion Style:
expect(foo).must_equal 100
require 'test_helper'
class UserTest < ActiveSupport::TestCase
  let(:user_ken)   { User.create! :email => '' }
  it 'works' do
    expect(user_ken).must_be_instance_of User
require 'test_helper'
describe User do

RSpec 3 is also moving away from the outer describe test type inference, as described in this line from their release notes.

Spec types are no longer inferred by location, they instead need to be explicitly tagged. The old behaviour is enabled by config.infer_spec_type_from_file_location!, which is still supplied in the default generated spec_helper.rb. (Xavier Shay, Myron Marston)

Not that we want to mimic RSpec, but the aim of this gem is very straight forward and minimalistic. We simply want to expose the Minitest Spec::DSL and core assertion style within ActiveSupport. Period. So it is very possible that us matching outer describe to classes is simply going to go away one day soon.

Just for reference, here is a full list of each of Rails test case we support.

# Model Test (or anything else not listed below)
class UserTest < ActiveSupport::TestCase

# Controller Test
class UsersControllerTest < ActionController::TestCase

# Integration Tests - Must use subclass style!
class IntegrationTest < ActionDispatch::IntegrationTest

# Mailer Test
class UserMailerTest < ActionMailer::TestCase

# View Helper Test
class UsersHelperTest < ActionView::TestCase

# Job Helper Test
class MyJobTest < ActiveJob::TestCase


We have baked in a few extra methods behind the scenes to minitest-spec-rails. Most directly support our needs to reflect on described classes, however, they may be useful to you too when meta-programming on top of minitest-spec-rails.


The described_class method is available both via a class method and an instance method in any Rails test case. It is guaranteed to work despite the described level too. This allows class level macros to be built, much like Shoulda. Remember, it can only do this if you follow Rails naming conventions for your tests.

class UserTest < ActiveSupport::TestCase
  described_class # => User(id: integer, email: string)
  it 'works here' do
    described_class # => User(id: integer, email: string)
  describe 'and' do
    it 'works here too' do
      described_class # => User(id: integer, email: string)

Setup & Teardown Compatability

Rails ActiveSupport::TestCase allows multiple setup and teardown methods per class. It also allows you to specify these either with a symbol or a block. Unlike normal ActiveSupport setup and teardown callbacks, our blocks are evaluated in the scope of the instance, just like before and after. So this just works!

class ActiveSupportCallbackTest < ActiveSupport::TestCase

  setup :foo
  setup :bar
  before { @bat = 'biz' }

  it 'works' do
    expect(@foo).must_equal 'foo'
    expect(@bar).must_equal 'bar'
    expect(@bat).must_equal 'biz'


  def foo ; @foo = 'foo' ; end
  def bar ; @bar = 'bar' ; end



If you are migrating away from Shoulda, then minitest-spec-rails' mini_shoulda feature will help. To enable it, set the following configuration in your test environment file.

# In config/environments/test.rb
config.minitest_spec_rails.mini_shoulda = true

Doing so only enables a few aliases that allow the Shoulda context, should, and should_eventually methods. The following code demonstrates the full features of the mini_shoulda implementation. It basically replaces the shell of shoulda-context in a few lines of code.

class PostTests < ActiveSupport::TestCase
  setup    { @post = Post.create! :title => 'Test Title', :body => 'Test body' }
  teardown { Post.delete_all }
  should 'work' do
    @post.must_be_instance_of Post
  context 'with a user' do
    should_eventually 'have a user' do
      # ...

If you prefer the assertions provided by shoulda-context like assert_same_elements, then you may want to consider copying them from here and including them in MiniTest::Spec yourself. I personally recommend just replacing these assertions with something more modern. A few examples are below.

assert_same_elements a, b         # From
expect(a.sort).must_equal b.sort  # To

assert_does_not_contain a, b  # From
expect(a).wont_include b      # To


I highly suggest that you stay away from matchers since MiniTest::Spec gives you all the tools you need to write good tests. Staying away from matchers will make your code's tests live longer. So my advice is to stay away from things like .should == and just write .must_equal instead. However, if matchers are really your thing, I recommend the minitest-matchers gem. You can also check out the valid_attribute gem built on top of minitest-matchers.

describe Post do
  subject { }
  it { must have_valid(:title).when("Hello") }
  it { wont have_valid(:title).when("", nil, "Bad") }

Alternatively, try the mintest-matchers_vaccine gem to avoid infecting the objects that you want to test.

describe User do
  subject { }
  it "should validate email" do
    must have_valid(:email).when("", "")
    wont have_valid(:email).when(nil, "", "foo", "foo@bar")


Assertion Methods

If you are upgrading from Test::Unit, there are a few missing assertions that have been renamed or are no longer available within MiniTest.

  • The method assert_raise is renamed assert_raises.
  • There is no method assert_nothing_raised. There are good reasons for this on Ryan's blog entry.


If you are using Mocha for mocking and stubbing, please update to the latest, 0.13.1 or higher so it is compatible with the latest MiniTest. If you do not like the deprecation warnings in older versions of Rails, just add this below the require 'rails/all' within your application.rb file :)

require 'mocha/deprecation'
Mocha::Deprecation.mode = :disabled

Rails 3.0.x

If you are using minitest-spec-rails with Rails 3.0, then your controller and mailer tests will need to use the tests interface for the assertions to be setup correctly within sub describe blocks. I think this is a bug with class_attribute within Rails 3.0 only. So use the following patterns.

class UsersControllerTest < ActionController::TestCase
  tests UsersController
class UserMailerTest < ActionMailer::TestCase
  tests UserMailer

Rails 3.1 & 3.2

If your view helper tests give you an eror like this: RuntimeError: In order to use #url_for, you must include routing helpers explicitly., this is something that is broken only for Rails 3.1 and 3.2, both 3.0 and 4.0 and above do not exhibit this error. I have heard that if you include Rails.application.routes.url_helpers in your tests or inject them into the helper module before the test it may work. Lemme know what you find out.


We run our tests on GitHub Actions. If you detect a problem, open up a github issue or fork the repo and help out. After you fork or clone the repository, the following commands will get you up and running on the test suite.

$ bundle install
$ bundle exec appraisal update
$ bundle exec appraisal rake test

We use the appraisal gem from Thoughtbot to help us generate the individual gemfiles for each Rails version and to run the tests locally against each generated Gemfile. The rake appraisal test command actually runs our test suite against all Rails versions in our Appraisal file. If you want to run the tests for a specific Rails version, use bundle exec appraisal -h for a list. For example, the following command will run the tests for Rails 4.1 only.

$ bundle exec appraisal rails_v6.0.x rake test
$ bundle exec appraisal rails_v6.1.x rake test
$ bundle exec appraisal rails_v7.0.x rake test

We have a few branches for each major Rails version.

  • 2-3-stable - Tracks Rails 2.3.x with MiniTest 4.x.
  • 3-x-stable - Oddly tracks Rails 3.x and 4.0 with MiniTest 4.x.
  • master - Currently tracks Rails 4.1 which uses Minitest 5.0.