Testing Rails Applications

1. Why Write Tests?

Writing automated tests can be a faster way of ensuring your code continues to work as expected than manual testing through the browser or the console. Failing tests can quickly reveal issues, allowing you to identify and fix bugs early in the development process. This practice not only improves the reliability of your code but also improves confidence in your changes.

Rails makes it easy to write tests. You can read more about Rails' built in support for testing in the next section.

2. Introduction to Testing

With Rails, testing is central to the development process right from the creation of a new application.

2.1. Test Setup

Rails creates a test directory for you as soon as you create a Rails project using bin/rails new application_name. If you list the contents of this directory then you will see:

$ ls -F test
application_system_test_case.rb  controllers/                     helpers/                         mailers/                         system/                          fixtures/                        integration/                     models/                          test_helper.rb

2.2. Test Directories

The helpers, mailers, and models directories store tests for view helpers, mailers, and models, respectively.

The controllers directory is used for tests related to controllers, routes, and views, where HTTP requests will be simulated and assertions made on the outcomes.

The integration directory is reserved for tests that cover interactions between controllers.

The system test directory holds system tests, which are used for full browser testing of your application. System tests allow you to test your application the way your users experience it and help you test your JavaScript as well. System tests inherit from Capybara and perform in-browser tests for your application.

Fixtures are a way of mocking up data to use in your tests, so that you don't have to use 'real' data. They are stored in the fixtures directory, and you can read more about them in the Fixtures section below.

A jobs directory will also be created for your job tests when you first generate a job.

The test_helper.rb file holds the default configuration for your tests.

The application_system_test_case.rb holds the default configuration for your system tests.

2.3. The Test Environment

By default, every Rails application has three environments: development, test, and production.

Each environment's configuration can be modified similarly. In this case, we can modify our test environment by changing the options found in config/environments/test.rb.

2.4. Writing Your First Test

We introduced the bin/rails generate model command in the Getting Started with Rails guide. Alongside creating a model, this command also creates a test stub in the test directory:

$ bin/rails generate model article title:string body:text
...
create  app/models/article.rb
create  test/models/article_test.rb
...

The default test stub in test/models/article_test.rb looks like this:

require "test_helper"

class ArticleTest < ActiveSupport::TestCase
  # test "the truth" do
  #   assert true
  # end
end

A line by line examination of this file will help get you oriented to Rails testing code and terminology.

require "test_helper"

Requiring the file, test_helper.rb, loads the default configuration to run tests. All methods added to this file are also available in tests when this file is included.

class ArticleTest < ActiveSupport::TestCase
  # ...
end

This is called a test case, because the ArticleTest class inherits from ActiveSupport::TestCase. It therefore also has all the methods from ActiveSupport::TestCase available to it. Later in this guide, we'll see some of the methods this gives us.

Any method defined within a class inherited from Minitest::Test (which is the superclass of ActiveSupport::TestCase) that begins with test_ is simply called a test. So, methods defined as test_password and test_valid_password are test names and are run automatically when the test case is run.

Rails also adds a test method that takes a test name and a block. It generates a standard Minitest::Unit test with method names prefixed with test_, allowing you to focus on writing the test logic without having to think about naming the methods. For example, you can write:

test "the truth" do
  assert true
end

Which is approximately the same as writing this:

def test_the_truth
  assert true
end

Although you can still use regular method definitions, using the test macro allows for a more readable test name.

This part of a test is called an 'assertion':

assert true

An assertion is a line of code that evaluates an object (or expression) for expected results. For example, an assertion can check:

• does this value equal that value?
• is this object nil?
• does this line of code throw an exception?
• is the user's password greater than 5 characters?

Every test may contain one or more assertions, with no restriction as to how many assertions are allowed. Only when all the assertions are successful will the test pass.

2.4.1. Your First Failing Test

To see how a test failure is reported, you can add a failing test to the article_test.rb test case. In this example, it is asserted that the article will not save without meeting certain criteria; hence, if the article saves successfully, the test will fail, demonstrating a test failure.

require "test_helper"

class ArticleTest < ActiveSupport::TestCase
  test "should not save article without title" do
    article = Article.new
    assert_not article.save
  end
end

Here is the output if this newly added test is run:

$ bin/rails test test/models/article_test.rb
Running 1 tests in a single process (parallelization threshold is 50)
Run options: --seed 44656

# Running:

F

Failure:
ArticleTest#test_should_not_save_article_without_title [/path/to/blog/test/models/article_test.rb:4]:
Expected true to be nil or false


bin/rails test test/models/article_test.rb:4



Finished in 0.023918s, 41.8090 runs/s, 41.8090 assertions/s.

1 runs, 1 assertions, 1 failures, 0 errors, 0 skips

In the output, F indicates a test failure. The section under Failure includes the name of the failing test, followed by a stack trace and a message showing the actual value and the expected value from the assertion. The default assertion messages offer just enough information to help identify the error. For improved readability, every assertion allows an optional message parameter to customize the failure message, as shown below:

test "should not save article without title" do
  article = Article.new
  assert_not article.save, "Saved the article without a title"
end

Running this test shows the friendlier assertion message:

Failure:
ArticleTest#test_should_not_save_article_without_title [/path/to/blog/test/models/article_test.rb:6]:
Saved the article without a title

To get this test to pass a model-level validation can be added for the title field.

class Article < ApplicationRecord
  validates :title, presence: true
end

Now the test should pass, as the article in our test has not been initialized with a title, so the model validation will prevent the save. This can be verified by running the test again:

$ bin/rails test test/models/article_test.rb:6
Running 1 tests in a single process (parallelization threshold is 50)
Run options: --seed 31252

# Running:

.

Finished in 0.027476s, 36.3952 runs/s, 36.3952 assertions/s.

1 runs, 1 assertions, 0 failures, 0 errors, 0 skips

The small green dot displayed means that the test has passed successfully.

2.4.2. Reporting Errors

To see how an error gets reported, here's a test containing an error:

test "should report error" do
  # some_undefined_variable is not defined elsewhere in the test case
  some_undefined_variable
  assert true
end

Now you can see even more output in the console from running the tests:

$ bin/rails test test/models/article_test.rb
Running 2 tests in a single process (parallelization threshold is 50)
Run options: --seed 1808

# Running:

E

Error:
ArticleTest#test_should_report_error:
NameError: undefined local variable or method 'some_undefined_variable' for #<ArticleTest:0x007fee3aa71798>
    test/models/article_test.rb:11:in 'block in <class:ArticleTest>'


bin/rails test test/models/article_test.rb:9

.

Finished in 0.040609s, 49.2500 runs/s, 24.6250 assertions/s.

2 runs, 1 assertions, 0 failures, 1 errors, 0 skips

Notice the 'E' in the output. It denotes a test with an error. The green dot above the 'Finished' line denotes the one passing test.

When a test fails you are presented with the corresponding backtrace. By default, Rails filters the backtrace and will only print lines relevant to your application. This eliminates noise and helps you to focus on your code. However, in situations when you want to see the full backtrace, set the -b (or --backtrace) argument to enable this behavior:

$ bin/rails test -b test/models/article_test.rb

If you want this test to pass you can modify it to use assert_raises (so you are now checking for the presence of the error) like so:

test "should report error" do
  # some_undefined_variable is not defined elsewhere in the test case
  assert_raises(NameError) do
    some_undefined_variable
  end
end

This test should now pass.

2.5. Minitest Assertions

By now you've caught a glimpse of some of the assertions that are available. Assertions are the foundation blocks of testing. They are the ones that actually perform the checks to ensure that things are going as planned.

Here's an extract of the assertions you can use with minitest, the default testing library used by Rails. The [msg] parameter is an optional string message you can specify to make your test failure messages clearer.

The above are a subset of assertions that minitest supports. For an exhaustive and more up-to-date list, please check the minitest API documentation, specifically Minitest::Assertions.

With minitest you can add your own assertions. In fact, that's exactly what Rails does. It includes some specialized assertions to make your life easier.

2.6. Rails-Specific Assertions

Rails adds some custom assertions of its own to the minitest framework:

You'll see the usage of some of these assertions in the next chapter.

2.7. Assertions in Test Cases

All the basic assertions such as assert_equal defined in Minitest::Assertions are also available in the classes we use in our own test cases. In fact, Rails provides the following classes for you to inherit from:

• ActiveSupport::TestCase
• ActionMailer::TestCase
• ActionView::TestCase
• ActiveJob::TestCase
• ActionDispatch::Integration::Session
• ActionDispatch::SystemTestCase
• Rails::Generators::TestCase

Each of these classes include Minitest::Assertions, allowing us to use all of the basic assertions in your tests.

2.8. The Rails Test Runner

We can run all of our tests at once by using the bin/rails test command.

Or we can run a single test file by appending the filename to the bin/rails test command.

$ bin/rails test test/models/article_test.rb
Running 1 tests in a single process (parallelization threshold is 50)
Run options: --seed 1559

# Running:

..

Finished in 0.027034s, 73.9810 runs/s, 110.9715 assertions/s.

2 runs, 3 assertions, 0 failures, 0 errors, 0 skips

This will run all test methods from the test case.

You can also run a particular test method from the test case by providing the -n or --name flag and the test's method name.

$ bin/rails test test/models/article_test.rb -n test_the_truth
Running 1 tests in a single process (parallelization threshold is 50)
Run options: -n test_the_truth --seed 43583

# Running:

.

Finished tests in 0.009064s, 110.3266 tests/s, 110.3266 assertions/s.

1 tests, 1 assertions, 0 failures, 0 errors, 0 skips

You can also run a test at a specific line by providing the line number.

$ bin/rails test test/models/article_test.rb:6 # run specific test and line

You can also run a range of tests by providing the line range.

$ bin/rails test test/models/article_test.rb:6-20 # runs tests from line 6 to 20

You can also run an entire directory of tests by providing the path to the directory.

$ bin/rails test test/controllers # run all tests from specific directory

The test runner also provides a lot of other features like failing fast, showing verbose progress, and so on. Check the documentation of the test runner using the command below:

$ bin/rails test -h
Usage:
  bin/rails test [PATHS...]

Run tests except system tests

Examples:
    You can run a single test by appending a line number to a filename:

        bin/rails test test/models/user_test.rb:27

    You can run multiple tests with in a line range by appending the line range to a filename:

        bin/rails test test/models/user_test.rb:10-20

    You can run multiple files and directories at the same time:

        bin/rails test test/controllers test/integration/login_test.rb

    By default test failures and errors are reported inline during a run.

minitest options:
    -h, --help                       Display this help.
        --no-plugins                 Bypass minitest plugin auto-loading (or set $MT_NO_PLUGINS).
    -s, --seed SEED                  Sets random seed. Also via env. Eg: SEED=n rake
    -v, --verbose                    Verbose. Show progress processing files.
        --show-skips                 Show skipped at the end of run.
    -n, --name PATTERN               Filter run on /regexp/ or string.
        --exclude PATTERN            Exclude /regexp/ or string from run.
    -S, --skip CODES                 Skip reporting of certain types of results (eg E).

Known extensions: rails, pride
    -w, --warnings                   Run with Ruby warnings enabled
    -e, --environment ENV            Run tests in the ENV environment
    -b, --backtrace                  Show the complete backtrace
    -d, --defer-output               Output test failures and errors after the test run
    -f, --fail-fast                  Abort test run on first failure or error
    -c, --[no-]color                 Enable color in the output
        --profile [COUNT]            Enable profiling of tests and list the slowest test cases (default: 10)
    -p, --pride                      Pride. Show your testing pride!

3. The Test Database

Just about every Rails application interacts heavily with a database and so your tests will need a database to interact with as well. This section covers how to set up this test database and populate it with sample data.

As mentioned in the Test Envionment section, every Rails application has three environments: development, test, and production. The database for each one of them is configured in config/database.yml.

A dedicated test database allows you to set up and interact with test data in isolation. This way your tests can interact with test data with confidence, without worrying about the data in the development or production databases.

3.1. Maintaining the Test Database Schema

In order to run your tests, your test database needs the current schema. The test helper checks whether your test database has any pending migrations. It will try to load your db/schema.rb or db/structure.sql into the test database. If migrations are still pending, an error will be raised. Usually this indicates that your schema is not fully migrated. Running the migrations (using bin/rails db:migrate RAILS_ENV=test) will bring the schema up to date.

3.2. Fixtures

For good tests, you'll need to give some thought to setting up test data. In Rails, you can handle this by defining and customizing fixtures. You can find comprehensive documentation in the Fixtures API documentation.

3.2.1. What are Fixtures?

Fixtures is a fancy word for a consistent set of test data. Fixtures allow you to populate your testing database with predefined data before your tests run. Fixtures are database independent and written in YAML. There is one file per model.

Fixtures are stored in your test/fixtures directory.

3.2.2. YAML

YAML is a human-readable data serialization language. YAML-formatted fixtures are a human-friendly way to describe your sample data. These types of fixtures have the .yml file extension (as in users.yml).

Here's a sample YAML fixture file:

# lo & behold! I am a YAML comment!
david:
  name: David Heinemeier Hansson
  birthday: 1979-10-15
  profession: Systems development

steve:
  name: Steve Ross Kellock
  birthday: 1974-09-27
  profession: guy with keyboard

Each fixture is given a name followed by an indented list of colon-separated key/value pairs. Records are typically separated by a blank line. You can place comments in a fixture file by using the # character in the first column.

If you are working with associations, you can define a reference node between two different fixtures. Here's an example with a belongs_to/has_many association:

# test/fixtures/categories.yml
web_frameworks:
  name: Web Frameworks

# test/fixtures/articles.yml
first:
  title: Welcome to Rails!
  category: web_frameworks

# test/fixtures/action_text/rich_texts.yml
first_content:
  record: first (Article)
  name: content
  body: <div>Hello, from <strong>a fixture</strong></div>

Notice the category key of the first Article found in fixtures/articles.yml has a value of web_frameworks, and that the record key of the first_content entry found in fixtures/action_text/rich_texts.yml has a value of first (Article). This hints to Active Record to load the Category web_frameworks found in fixtures/categories.yml for the former, and Action Text to load the Article first found in fixtures/articles.yml for the latter.

3.2.3. File Attachment Fixtures

Like other Active Record-backed models, Active Storage attachment records inherit from ActiveRecord::Base instances and can therefore be populated by fixtures.

Consider an Article model that has an associated image as a thumbnail attachment, along with fixture data YAML:

class Article < ApplicationRecord
  has_one_attached :thumbnail
end

# test/fixtures/articles.yml
first:
  title: An Article

Assuming that there is an image/png encoded file at test/fixtures/files/first.png, the following YAML fixture entries will generate the related ActiveStorage::Blob and ActiveStorage::Attachment records:

# test/fixtures/active_storage/blobs.yml
first_thumbnail_blob: <%= ActiveStorage::FixtureSet.blob filename: "first.png" %>

# test/fixtures/active_storage/attachments.yml
first_thumbnail_attachment:
  name: thumbnail
  record: first (Article)
  blob: first_thumbnail_blob

3.2.4. Embedding Code in Fixtures

ERB allows you to embed Ruby code within templates. The YAML fixture format is pre-processed with ERB when Rails loads fixtures. This allows you to use Ruby to help you generate some sample data. For example, the following code generates a thousand users:

<% 1000.times do |n| %>
  user_<%= n %>:
    username: <%= "user#{n}" %>
    email: <%= "user#{n}@example.com" %>
<% end %>

3.2.5. Fixtures in Action

Rails automatically loads all fixtures from the test/fixtures directory by default. Loading involves three steps:

1. Remove any existing data from the table corresponding to the fixture
2. Load the fixture data into the table
3. Dump the fixture data into a method in case you want to access it directly

3.2.6. Fixtures are Active Record Objects

Fixtures are instances of Active Record. As mentioned above, you can access the object directly because it is automatically available as a method whose scope is local to the test case. For example:

# this will return the User object for the fixture named david
users(:david)

# this will return the property for david called id
users(:david).id

# methods available to the User object can also be accessed
david = users(:david)
david.call(david.partner)

To get multiple fixtures at once, you can pass in a list of fixture names. For example:

# this will return an array containing the fixtures david and steve
users(:david, :steve)

3.3. Transactions

By default, Rails automatically wraps tests in a database transaction that is rolled back once completed. This makes tests independent of each other and means that changes to the database are only visible within a single test.

class MyTest < ActiveSupport::TestCase
  test "newly created users are active by default" do
    # Since the test is implicitly wrapped in a database transaction, the user
    # created here won't be seen by other tests.
    assert User.create.active?
  end
end

The method ActiveRecord::Base.current_transaction still acts as intended, though:

class MyTest < ActiveSupport::TestCase
  test "Active Record current_transaction method works as expected" do
    # The implicit transaction around tests does not interfere with the
    # application-level semantics of the current_transaction.
    assert User.current_transaction.blank?
  end
end

If there are multiple writing databases in place, tests are wrapped in as many respective transactions, and all of them are rolled back.

3.3.1. Opting-out of Test Transactions

Individual test cases can opt-out:

class MyTest < ActiveSupport::TestCase
  # No implicit database transaction wraps the tests in this test case.
  self.use_transactional_tests = false
end

4. Testing Models

Model tests are used to test the models of your application and their associated logic. You can test this logic using the assertions and fixtures that we've explored in the sections above.

Rails model tests are stored under the test/models directory. Rails provides a generator to create a model test skeleton for you.

$ bin/rails generate test_unit:model article
create  test/models/article_test.rb

This command will generate the following file:

# article_test.rb
require "test_helper"

class ArticleTest < ActiveSupport::TestCase
  # test "the truth" do
  #   assert true
  # end
end

Model tests don't have their own superclass like ActionMailer::TestCase. Instead, they inherit from ActiveSupport::TestCase.

5. Functional Testing for Controllers

When writing functional tests, you are focusing on testing how controller actions handle the requests and the expected result or response. Functional controller tests are sometimes used in cases where system tests are not appropriate, e.g., to confirm an API response.

5.1. What to Include in Your Functional Tests

You could test for things such as:

• was the web request successful?
• was the user redirected to the right page?
• was the user successfully authenticated?
• was the correct information displayed in the response?

The easiest way to see functional tests in action is to generate a controller using the scaffold generator:

$ bin/rails generate scaffold_controller article
...
create  app/controllers/articles_controller.rb
...
invoke  test_unit
create    test/controllers/articles_controller_test.rb
...

This will generate the controller code and tests for an Article resource. You can take a look at the file articles_controller_test.rb in the test/controllers directory.

If you already have a controller and just want to generate the test scaffold code for each of the seven default actions, you can use the following command:

$ bin/rails generate test_unit:scaffold article
...
invoke  test_unit
create    test/controllers/articles_controller_test.rb
...

Let's take a look at one such test, test_should_get_index from the file articles_controller_test.rb.

# articles_controller_test.rb
class ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "should get index" do
    get articles_url
    assert_response :success
  end
end

In the test_should_get_index test, Rails simulates a request on the action called index, making sure the request was successful, and also ensuring that the right response body has been generated.

The get method kicks off the web request and populates the results into the @response. It can accept up to 6 arguments:

• The URI of the controller action you are requesting. This can be in the form of a string or a route helper (e.g. articles_url).
• params: option with a hash of request parameters to pass into the action (e.g. query string parameters or article variables).
• headers: for setting the headers that will be passed with the request.
• env: for customizing the request environment as needed.
• xhr: whether the request is AJAX request or not. Can be set to true for marking the request as AJAX.
• as: for encoding the request with different content type.

All of these keyword arguments are optional.

Example: Calling the :show action (via a get request) for the first Article, passing in an HTTP_REFERER header:

get article_url(Article.first), headers: { "HTTP_REFERER" => "http://example.com/home" }

Another example: Calling the :update action (via a patch request) for the last Article, passing in new text for the title in params, as an AJAX request:

patch article_url(Article.last), params: { article: { title: "updated" } }, xhr: true

One more example: Calling the :create action (via a post request) to create a new article, passing in text for the title in params, as JSON request:

post articles_url, params: { article: { title: "Ahoy!" } }, as: :json

Now to modify the test_should_create_article test in articles_controller_test.rb so that this test passes:

test "should create article" do
  assert_difference("Article.count") do
    post articles_url, params: { article: { body: "Rails is awesome!", title: "Hello Rails" } }
  end

  assert_redirected_to article_path(Article.last)
end

You can now run this test and it will pass.

post articles_url, params: { article: { body: "Rails is awesome!", title: "Hello Rails" } }, headers: { Authorization: ActionController::HttpAuthentication::Basic.encode_credentials("dhh", "secret") }

5.2. HTTP Request Types for Functional Tests

If you're familiar with the HTTP protocol, you'll know that get is a type of request. There are 6 request types supported in Rails functional tests:

• get
• post
• patch
• put
• head
• delete

All of the request types have equivalent methods that you can use. In a typical CRUD application you'll be using post, get, put, and delete most often.

5.3. Testing XHR (AJAX) Requests

An AJAX request (Asynchronous Javscript and XML) is a technique where content is fetched from the server using asynchronous HTTP requests and the relevant parts of the page are updated without requiring a full page load.

To test AJAX requests, you can specify the xhr: true option to get, post, patch, put, and delete methods. For example:

test "AJAX request" do
  article = articles(:one)
  get article_url(article), xhr: true

  assert_equal "hello world", @response.body
  assert_equal "text/javascript", @response.media_type
end

5.4. Testing Other Request Objects

After any request has been made and processed, you will have 3 Hash objects ready for use:

• cookies - Any cookies that are set
• flash - Any objects living in the flash
• session - Any object living in session variables

As is the case with normal Hash objects, you can access the values by referencing the keys by string. You can also reference them by symbol name. For example:

flash["gordon"]               # or flash[:gordon]
session["shmession"]          # or session[:shmession]
cookies["are_good_for_u"]     # or cookies[:are_good_for_u]

5.5. Instance Variables

You also have access to three instance variables in your functional tests after a request is made:

• @controller - The controller processing the request
• @request - The request object
• @response - The response object

class ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "should get index" do
    get articles_url

    assert_equal "index", @controller.action_name
    assert_equal "application/x-www-form-urlencoded", @request.media_type
    assert_match "Articles", @response.body
  end
end

5.6. Setting Headers and CGI Variables

HTTP headers are pieces of information sent along with HTTP requests to provide important metadata. CGI variables are environment variables used to exchange information between the web server and the application.

HTTP headers and CGI variables can be tested by being passed as headers:

# setting an HTTP Header
get articles_url, headers: { "Content-Type": "text/plain" } # simulate the request with custom header

# setting a CGI variable
get articles_url, headers: { "HTTP_REFERER": "http://example.com/home" } # simulate the request with custom env variable

5.7. Testing flash Notices

As can be seen in the testing other request objects section, one of the three hash objects that is accessible in the tests is flash. This section outlines how to test the appearance of a flash message in our blog application whenever someone successfully creates a new article.

First, an assertion should be added to the test_should_create_article test:

test "should create article" do
  assert_difference("Article.count") do
    post articles_url, params: { article: { title: "Some title" } }
  end

  assert_redirected_to article_path(Article.last)
  assert_equal "Article was successfully created.", flash[:notice]
end

If the test is run now, it should fail:

$ bin/rails test test/controllers/articles_controller_test.rb -n test_should_create_article
Running 1 tests in a single process (parallelization threshold is 50)
Run options: -n test_should_create_article --seed 32266

# Running:

F

Finished in 0.114870s, 8.7055 runs/s, 34.8220 assertions/s.

  1) Failure:
ArticlesControllerTest#test_should_create_article [/test/controllers/articles_controller_test.rb:16]:
--- expected
+++ actual
@@ -1 +1 @@
-"Article was successfully created."
+nil

1 runs, 4 assertions, 1 failures, 0 errors, 0 skips

Now implement the flash message in the controller. The :create action should look like this:

def create
  @article = Article.new(article_params)

  if @article.save
    flash[:notice] = "Article was successfully created."
    redirect_to @article
  else
    render "new"
  end
end

Now, if the tests are run they should pass:

$ bin/rails test test/controllers/articles_controller_test.rb -n test_should_create_article
Running 1 tests in a single process (parallelization threshold is 50)
Run options: -n test_should_create_article --seed 18981

# Running:

.

Finished in 0.081972s, 12.1993 runs/s, 48.7972 assertions/s.

1 runs, 4 assertions, 0 failures, 0 errors, 0 skips

5.8. Tests for show, update, and delete Actions

So far in the guide tests for the :index as well as the:create action have been outlined. What about the other actions?

You can write a test for :show as follows:

test "should show article" do
  article = articles(:one)
  get article_url(article)
  assert_response :success
end

If you remember from our discussion earlier on fixtures, the articles() method will provide access to the articles fixtures.

How about deleting an existing article?

test "should delete article" do
  article = articles(:one)
  assert_difference("Article.count", -1) do
    delete article_url(article)
  end

  assert_redirected_to articles_path
end

Here is a test for updating an existing article:

test "should update article" do
  article = articles(:one)

  patch article_url(article), params: { article: { title: "updated" } }

  assert_redirected_to article_path(article)
  # Reload article to refresh data and assert that title is updated.
  article.reload
  assert_equal "updated", article.title
end

Notice that there is some duplication in these three tests - they both access the same article fixture data. It is possible to DRY ('Don't Repeat Yourself') the implementation by using the setup and teardown methods provided by ActiveSupport::Callbacks.

The tests might look like this:

require "test_helper"

class ArticlesControllerTest < ActionDispatch::IntegrationTest
  # called before every single test
  setup do
    @article = articles(:one)
  end

  # called after every single test
  teardown do
    # when controller is using cache it may be a good idea to reset it afterwards
    Rails.cache.clear
  end

  test "should show article" do
    # Reuse the @article instance variable from setup
    get article_url(@article)
    assert_response :success
  end

  test "should destroy article" do
    assert_difference("Article.count", -1) do
      delete article_url(@article)
    end

    assert_redirected_to articles_path
  end

  test "should update article" do
    patch article_url(@article), params: { article: { title: "updated" } }

    assert_redirected_to article_path(@article)
    # Reload association to fetch updated data and assert that title is updated.
    @article.reload
    assert_equal "updated", @article.title
  end
end

6. Integration Testing

Integration tests take functional controller tests one step further - they focus on testing how several parts of an application interact, and are generally used to test important workflows. Rails integration tests are stored in the test/integration directory.

Rails provides a generator to create an integration test skeleton as follows:

$ bin/rails generate integration_test user_flows
      invoke  test_unit
      create  test/integration/user_flows_test.rb

Here's what a freshly generated integration test looks like:

require "test_helper"

class UserFlowsTest < ActionDispatch::IntegrationTest
  # test "the truth" do
  #   assert true
  # end
end

Here the test is inheriting from ActionDispatch::IntegrationTest. This makes some additional helpers available for integration tests alongside the standard testing helpers.

6.1. Implementing an Integration Test

Let's add an integration test to our blog application, by starting with a basic workflow of creating a new blog article to verify that everything is working properly.

Start by generating the integration test skeleton:

$ bin/rails generate integration_test blog_flow

It should have created a test file placeholder. With the output of the previous command you should see:

      invoke  test_unit
      create    test/integration/blog_flow_test.rb

Now open that file and write the first assertion:

require "test_helper"

class BlogFlowTest < ActionDispatch::IntegrationTest
  test "can see the welcome page" do
    get "/"
    assert_selector "h1", "Welcome#index"
  end
end

If you visit the root path, you should see welcome/index.html.erb rendered for the view. So this assertion should pass.

6.1.1. Creating Articles Integration

To test the ability to create a new article in our blog and display the resulting article, see the example below:

test "can create an article" do
  get "/articles/new"
  assert_response :success

  post "/articles",
    params: { article: { title: "can create", body: "article successfully." } }
  assert_response :redirect
  follow_redirect!
  assert_response :success
  assert_dom "p", "Title:\n  can create"
end

The :new action of our Articles controller is called first, and the response should be successful.

Next, a post request is made to the :create action of the Articles controller:

post "/articles",
  params: { article: { title: "can create", body: "article successfully." } }
assert_response :redirect
follow_redirect!

The two lines following the request are to handle the redirect setup when creating a new article.

Finally it can be asserted that the response was successful and the newly-created article is readable on the page.

A very small workflow for visiting our blog and creating a new article was successfully tested above. To extend this, additional tests could be added for features like adding comments, editing comments or removing articles. Integration tests are a great place to experiment with all kinds of use cases for our applications.

6.2. Helpers Available for Integration Tests

There are numerous helpers to choose from for use in integration tests. Some include:

• ActionDispatch::Integration::Runner for helpers relating to the integration test runner, including creating a new session.

• ActionDispatch::Integration::RequestHelpers for performing requests.

• ActionDispatch::TestProcess::FixtureFile for uploading files.

• ActionDispatch::Integration::Session to modify sessions or the state of the integration tests.

7. System Testing

Similarly to integration testing, system testing allows you to test how the components of your app work together, but from the point of view of a user. It does this by running tests in either a real or a headless browser (a browser which runs in the background without opening a visible window). System tests use Capybara under the hood.

Rails system tests are stored in the test/system directory in your application. To generate a system test skeleton, run the following command:

$ bin/rails generate system_test users
      invoke test_unit
      create test/system/users_test.rb

Here's what a freshly generated system test looks like:

require "application_system_test_case"

class UsersTest < ApplicationSystemTestCase
  # test "visiting the index" do
  #   visit users_url
  #
  #   assert_selector "h1", text: "Users"
  # end
end

By default, system tests are run with the Selenium driver, using the Chrome browser, and a screen size of 1400x1400. The next section explains how to change the default settings.

7.1. Changing the Default Settings

Rails makes changing the default settings for system tests very simple. All the setup is abstracted away so you can focus on writing your tests.

When you generate a new application or scaffold, an application_system_test_case.rb file is created in the test directory. This is where all the configuration for your system tests should live.

If you want to change the default settings, you can change what the system tests are "driven by". If you want to change the driver from Selenium to Cuprite, you'd add the cuprite gem to your Gemfile. Then in your application_system_test_case.rb file you'd do the following:

require "test_helper"
require "capybara/cuprite"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :cuprite
end

The driver name is a required argument for driven_by. The optional arguments that can be passed to driven_by are :using for the browser (this will only be used by Selenium), :screen_size to change the size of the screen for screenshots, and :options which can be used to set options supported by the driver.

require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :firefox
end

If you want to use a headless browser, you could use Headless Chrome or Headless Firefox by adding headless_chrome or headless_firefox in the :using argument.

require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :headless_chrome
end

If you want to use a remote browser, e.g. Headless Chrome in Docker, you have to add a remote url and set browser as remote through options.

require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  url = ENV.fetch("SELENIUM_REMOTE_URL", nil)
  options = if url
    { browser: :remote, url: url }
  else
    { browser: :chrome }
  end
  driven_by :selenium, using: :headless_chrome, options: options
end

Now you should get a connection to the remote browser.

$ SELENIUM_REMOTE_URL=http://localhost:4444/wd/hub bin/rails test:system

If your application is remote, e.g. within a Docker container, Capybara needs more input about how to call remote servers.

require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  setup do
      Capybara.server_host = "0.0.0.0" # bind to all interfaces
      Capybara.app_host = "http://#{IPSocket.getaddress(Socket.gethostname)}" if ENV["SELENIUM_REMOTE_URL"].present?
    end
  # ...
end

Now you should get a connection to a remote browser and server, regardless if it is running in a Docker container or CI.

If your Capybara configuration requires more setup than provided by Rails, this additional configuration can be added into the application_system_test_case.rb file.

Please see Capybara's documentation for additional settings.

7.2. Implementing a System Test

This section will demonstrate how to add a system test to your application, which tests a visit to the index page to create a new blog article.

If you used the scaffold generator, a system test skeleton was automatically created for you. If you didn't use the scaffold generator, start by creating a system test skeleton.

$ bin/rails generate system_test articles

It should have created a test file placeholder. With the output of the previous command you should see:

      invoke  test_unit
      create    test/system/articles_test.rb

Now, let's open that file and write the first assertion:

require "application_system_test_case"

class ArticlesTest < ApplicationSystemTestCase
  test "viewing the index" do
    visit articles_path
    assert_selector "h1", text: "Articles"
  end
end

The test should see that there is an h1 on the articles index page and pass.

Run the system tests.

$ bin/rails test:system

7.2.1. Creating Articles System Test

Now you can test the flow for creating a new article.

test "should create Article" do
  visit articles_path

  click_on "New Article"

  fill_in "Title", with: "Creating an Article"
  fill_in "Body", with: "Created this article successfully!"

  click_on "Create Article"

  assert_text "Creating an Article"
end

The first step is to call visit articles_path. This will take the test to the articles index page.

Then the click_on "New Article" will find the "New Article" button on the index page. This will redirect the browser to /articles/new.

Then the test will fill in the title and body of the article with the specified text. Once the fields are filled in, "Create Article" is clicked on which will send a POST request to /articles/create.

This redirects the user back to the articles index page, and there it is asserted that the text from the new article's title is on the articles index page.

7.2.2. Testing for Multiple Screen Sizes

If you want to test for mobile sizes in addition to testing for desktop, you can create another class that inherits from ActionDispatch::SystemTestCase and use it in your test suite. In this example, a file called mobile_system_test_case.rb is created in the /test directory with the following configuration.

require "test_helper"

class MobileSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :chrome, screen_size: [375, 667]
end

To use this configuration, create a test inside test/system that inherits from MobileSystemTestCase. Now you can test your app using multiple different configurations.

require "mobile_system_test_case"

class PostsTest < MobileSystemTestCase
  test "visiting the index" do
    visit posts_url
    assert_selector "h1", text: "Posts"
  end
end

7.2.3. Capybara Assertions

Here's an extract of the assertions provided by Capybara which can be used in system tests.

7.2.4. Screenshot Helper

The ScreenshotHelper is a helper designed to capture screenshots of your tests. This can be helpful for viewing the browser at the point a test failed, or to view screenshots later for debugging.

Two methods are provided: take_screenshot and take_failed_screenshot. take_failed_screenshot is automatically included in before_teardown inside Rails.

The take_screenshot helper method can be included anywhere in your tests to take a screenshot of the browser.

7.2.5. Taking It Further

System testing is similar to integration testing in that it tests the user's interaction with your controller, model, and view, but system testing tests your application as if a real user were using it. With system tests, you can test anything that a user would do in your application such as commenting, deleting articles, publishing draft articles, etc.

8. Test Helpers

To avoid code duplication, you can add your own test helpers. Here is an example for signing in:

# test/test_helper.rb

module SignInHelper
  def sign_in_as(user)
    post sign_in_url(email: user.email, password: user.password)
  end
end

class ActionDispatch::IntegrationTest
  include SignInHelper
end

require "test_helper"

class ProfileControllerTest < ActionDispatch::IntegrationTest
  test "should show profile" do
    # helper is now reusable from any controller test case
    sign_in_as users(:david)

    get profile_url
    assert_response :success
  end
end

8.1. Using Separate Files

If you find your helpers are cluttering test_helper.rb, you can extract them into separate files. A good place to store them is test/lib or test/test_helpers.

# test/test_helpers/multiple_assertions.rb
module MultipleAssertions
  def assert_multiple_of_forty_two(number)
    assert (number % 42 == 0), "expected #{number} to be a multiple of 42"
  end
end

These helpers can then be explicitly required and included as needed:

require "test_helper"
require "test_helpers/multiple_assertions"

class NumberTest < ActiveSupport::TestCase
  include MultipleAssertions

  test "420 is a multiple of 42" do
    assert_multiple_of_forty_two 420
  end
end

They can also continue to be included directly into the relevant parent classes:

# test/test_helper.rb
require "test_helpers/sign_in_helper"

class ActionDispatch::IntegrationTest
  include SignInHelper
end

8.2. Eagerly Requiring Helpers

You may find it convenient to eagerly require helpers in test_helper.rb so your test files have implicit access to them. This can be accomplished using globbing, as follows

# test/test_helper.rb
Dir[Rails.root.join("test", "test_helpers", "**", "*.rb")].each { |file| require file }

This has the downside of increasing the boot-up time, as opposed to manually requiring only the necessary files in your individual tests.

9. Testing Routes

Like everything else in your Rails application, you can test your routes. Route tests are stored in test/controllers/ or are part of controller tests. If your application has complex routes, Rails provides a number of useful helpers to test them.

For more information on routing assertions available in Rails, see the API documentation for ActionDispatch::Assertions::RoutingAssertions.

10. Testing Views

Testing the response to your request by asserting the presence of key HTML elements and their content is one way to test the views of your application. Like route tests, view tests are stored in test/controllers/ or are part of controller tests.

10.1. Querying the HTML

Methods like assert_dom and assert_dom_equal allow you to query HTML elements of the response by using a simple yet powerful syntax.

assert_dom is an assertion that will return true if matching elements are found. For example, you could verify that the page title is "Welcome to the Rails Testing Guide" as follows:

assert_dom "title", "Welcome to the Rails Testing Guide"

You can also use nested assert_dom blocks for deeper investigation.

In the following example, the inner assert_dom for li.menu_item runs within the collection of elements selected by the outer block:

assert_dom "ul.navigation" do
  assert_dom "li.menu_item"
end

A collection of selected elements may also be iterated through so that assert_dom may be called separately for each element. For example, if the response contains two ordered lists, each with four nested list elements then the following tests will both pass.

assert_dom "ol" do |elements|
  elements.each do |element|
    assert_dom element, "li", 4
  end
end

assert_dom "ol" do
  assert_dom "li", 8
end

The assert_dom_equal method compares two HTML strings to see if they are equal:

assert_dom_equal '<a href="http://www.further-reading.com">Read more</a>',
  link_to("Read more", "http://www.further-reading.com")

For more advanced usage, refer to the rails-dom-testing documentation.

In order to integrate with rails-dom-testing, tests that inherit from ActionView::TestCase declare a document_root_element method that returns the rendered content as an instance of a Nokogiri::XML::Node:

test "renders a link to itself" do
  article = Article.create! title: "Hello, world"

  render "articles/article", article: article
  anchor = document_root_element.at("a")

  assert_equal article.name, anchor.text
  assert_equal article_url(article), anchor["href"]
end

If your application depends on Nokogiri >= 1.14.0 or higher, and minitest >= 5.18.0, document_root_element supports Ruby's Pattern Matching:

test "renders a link to itself" do
  article = Article.create! title: "Hello, world"

  render "articles/article", article: article
  anchor = document_root_element.at("a")
  url = article_url(article)

  assert_pattern do
    anchor => { content: "Hello, world", attributes: [{ name: "href", value: url }] }
  end
end

If you'd like to access the same Capybara-powered Assertions that your System Testing tests utilize, you can define a base class that inherits from ActionView::TestCase and transforms the document_root_element into a page method:

# test/view_partial_test_case.rb

require "test_helper"
require "capybara/minitest"

class ViewPartialTestCase < ActionView::TestCase
  include Capybara::Minitest::Assertions

  def page
    Capybara.string(rendered)
  end
end

# test/views/article_partial_test.rb

require "view_partial_test_case"

class ArticlePartialTest < ViewPartialTestCase
  test "renders a link to itself" do
    article = Article.create! title: "Hello, world"

    render "articles/article", article: article

    assert_link article.title, href: article_url(article)
  end
end

More information about the assertions included by Capybara can be found in the Capybara Assertions section.

10.2. Parsing View Content

Starting in Action View version 7.1, the rendered helper method returns an object capable of parsing the view partial's rendered content.

To transform the String content returned by the rendered method into an object, define a parser by calling register_parser. Calling register_parser :rss defines a rendered.rss helper method. For example, to parse rendered RSS content into an object with rendered.rss, register a call to RSS::Parser.parse:

register_parser :rss, -> rendered { RSS::Parser.parse(rendered) }

test "renders RSS" do
  article = Article.create!(title: "Hello, world")

  render formats: :rss, partial: article

  assert_equal "Hello, world", rendered.rss.items.last.title
end

By default, ActionView::TestCase defines a parser for:

• :html - returns an instance of Nokogiri::XML::Node
• :json - returns an instance of ActiveSupport::HashWithIndifferentAccess

test "renders HTML" do
  article = Article.create!(title: "Hello, world")

  render partial: "articles/article", locals: { article: article }

  assert_pattern { rendered.html.at("main h1") => { content: "Hello, world" } }
end

test "renders JSON" do
  article = Article.create!(title: "Hello, world")

  render formats: :json, partial: "articles/article", locals: { article: article }

  assert_pattern { rendered.json => { title: "Hello, world" } }
end

10.3. Additional View-Based Assertions

There are more assertions that are primarily used in testing views:

Here's an example of using assert_dom_email:

assert_dom_email do
  assert_dom "small", "Please click the 'Unsubscribe' link if you want to opt-out."
end

10.4. Testing View Partials

Partial templates - usually called "partials" - can break the rendering process into more manageable chunks. With partials, you can extract sections of code from your views to separate files and reuse them in multiple places.

View tests provide an opportunity to test that partials render content the way you expect. View partial tests can be stored in test/views/ and inherit from ActionView::TestCase.

To render a partial, call render like you would in a template. The content is available through the test-local rendered method:

class ArticlePartialTest < ActionView::TestCase
  test "renders a link to itself" do
    article = Article.create! title: "Hello, world"

    render "articles/article", article: article

    assert_includes rendered, article.title
  end
end

Tests that inherit from ActionView::TestCase also have access to assert_dom and the other additional view-based assertions provided by rails-dom-testing:

test "renders a link to itself" do
  article = Article.create! title: "Hello, world"

  render "articles/article", article: article

  assert_dom "a[href=?]", article_url(article), text: article.title
end

10.5. Testing View Helpers

A helper is a module where you can define methods which are available in your views.

In order to test helpers, all you need to do is check that the output of the helper method matches what you'd expect. Tests related to the helpers are located under the test/helpers directory.

Given we have the following helper:

module UsersHelper
  def link_to_user(user)
    link_to "#{user.first_name} #{user.last_name}", user
  end
end

We can test the output of this method like this:

class UsersHelperTest < ActionView::TestCase
  test "should return the user's full name" do
    user = users(:david)

    assert_dom_equal %{<a href="/user/#{user.id}">David Heinemeier Hansson</a>}, link_to_user(user)
  end
end

Moreover, since the test class extends from ActionView::TestCase, you have access to Rails' helper methods such as link_to or pluralize.

11. Testing Mailers

Your mailer classes - like every other part of your Rails application - should be tested to ensure that they are working as expected.

The goals of testing your mailer classes are to ensure that:

• emails are being processed (created and sent)
• the email content is correct (subject, sender, body, etc)
• the right emails are being sent at the right times

There are two aspects of testing your mailer, the unit tests and the functional tests. In the unit tests, you run the mailer in isolation with tightly controlled inputs and compare the output to a known value (a fixture). In the functional tests you don't so much test the details produced by the mailer; instead, you test that the controllers and models are using the mailer in the right way. You test to prove that the right email was sent at the right time.

11.1. Unit Testing

In order to test that your mailer is working as expected, you can use unit tests to compare the actual results of the mailer with pre-written examples of what should be produced.

11.1.1. Mailer Fixtures

For the purposes of unit testing a mailer, fixtures are used to provide an example of how the output should look. Because these are example emails, and not Active Record data like the other fixtures, they are kept in their own subdirectory apart from the other fixtures. The name of the directory within test/fixtures directly corresponds to the name of the mailer. So, for a mailer named UserMailer, the fixtures should reside in test/fixtures/user_mailer directory.

If you generated your mailer, the generator does not create stub fixtures for the mailers actions. You'll have to create those files yourself as described above.

11.1.2. The Basic Test Case

Here's a unit test to test a mailer named UserMailer whose action invite is used to send an invitation to a friend:

require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.create_invite("me@example.com",
                                     "friend@example.com", Time.now)

    # Send the email, then test that it got queued
    assert_emails 1 do
      email.deliver_now
    end

    # Test the body of the sent email contains what we expect it to
    assert_equal ["me@example.com"], email.from
    assert_equal ["friend@example.com"], email.to
    assert_equal "You have been invited by me@example.com", email.subject
    assert_equal read_fixture("invite").join, email.body.to_s
  end
end

In the test the email is created and the returned object is stored in the email variable. The first assert checks it was sent, then, in the second batch of assertions, the email contents are checked. The helper read_fixture is used to read in the content from this file.

Here's the content of the invite fixture:

Hi friend@example.com,

You have been invited.

Cheers!

11.1.3. Configuring the Delivery Method for Test

The line ActionMailer::Base.delivery_method = :test in config/environments/test.rb sets the delivery method to test mode so that the email will not actually be delivered (useful to avoid spamming your users while testing). Instead, the email will be appended to an array (ActionMailer::Base.deliveries).

11.1.4. Testing Enqueued Emails

You can use the assert_enqueued_email_with assertion to confirm that the email has been enqueued with all of the expected mailer method arguments and/or parameterized mailer parameters. This allows you to match any emails that have been enqueued with the deliver_later method.

As with the basic test case, we create the email and store the returned object in the email variable. The following examples include variations of passing arguments and/or parameters.

This example will assert that the email has been enqueued with the correct arguments:

require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.create_invite("me@example.com", "friend@example.com")

    # Test that the email got enqueued with the correct arguments
    assert_enqueued_email_with UserMailer, :create_invite, args: ["me@example.com", "friend@example.com"] do
      email.deliver_later
    end
  end
end

This example will assert that a mailer has been enqueued with the correct mailer method named arguments by passing a hash of the arguments as args:

require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.create_invite(from: "me@example.com", to: "friend@example.com")

    # Test that the email got enqueued with the correct named arguments
    assert_enqueued_email_with UserMailer, :create_invite,
    args: [{ from: "me@example.com", to: "friend@example.com" }] do
      email.deliver_later
    end
  end
end

This example will assert that a parameterized mailer has been enqueued with the correct parameters and arguments. The mailer parameters are passed as params and the mailer method arguments as args:

require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.with(all: "good").create_invite("me@example.com", "friend@example.com")

    # Test that the email got enqueued with the correct mailer parameters and arguments
    assert_enqueued_email_with UserMailer, :create_invite,
    params: { all: "good" }, args: ["me@example.com", "friend@example.com"] do
      email.deliver_later
    end
  end
end

This example shows an alternative way to test that a parameterized mailer has been enqueued with the correct parameters:

require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.with(to: "friend@example.com").create_invite

    # Test that the email got enqueued with the correct mailer parameters
    assert_enqueued_email_with UserMailer.with(to: "friend@example.com"), :create_invite do
      email.deliver_later
    end
  end
end

11.2. Functional and System Testing

Unit testing allows us to test the attributes of the email while functional and system testing allows us to test whether user interactions appropriately trigger the email to be delivered. For example, you can check that the invite friend operation is sending an email appropriately:

# Integration Test
require "test_helper"

class UsersControllerTest < ActionDispatch::IntegrationTest
  test "invite friend" do
    # Asserts the difference in the ActionMailer::Base.deliveries
    assert_emails 1 do
      post invite_friend_url, params: { email: "friend@example.com" }
    end
  end
end

# System Test
require "test_helper"

class UsersTest < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :headless_chrome

  test "inviting a friend" do
    visit invite_users_url
    fill_in "Email", with: "friend@example.com"
    assert_emails 1 do
      click_on "Invite"
    end
  end
end

12. Testing Jobs

Jobs can be tested in isolation (focusing on the job's behavior) and in context (focusing on the calling code's behavior).

12.1. Testing Jobs in Isolation

When you generate a job, an associated test file will also be generated in the test/jobs directory.

Here is a test you could write for a billing job:

require "test_helper"

class BillingJobTest < ActiveJob::TestCase
  test "account is charged" do
    perform_enqueued_jobs do
      BillingJob.perform_later(account, product)
    end
    assert account.reload.charged_for?(product)
  end
end

The default queue adapter for tests will not perform jobs until perform_enqueued_jobs is called. Additionally, it will clear all jobs before each test is run so that tests do not interfere with each other.

The test uses perform_enqueued_jobs and perform_later instead of perform_now so that if retries are configured, retry failures are caught by the test instead of being re-enqueued and ignored.

12.2. Testing Jobs in Context

It's good practice to test that jobs are correctly enqueued, for example, by a controller action. The ActiveJob::TestHelper module provides several methods that can help with this, such as assert_enqueued_with.

Here is an example that tests an account model method:

require "test_helper"

class AccountTest < ActiveSupport::TestCase
  include ActiveJob::TestHelper

  test "#charge_for enqueues billing job" do
    assert_enqueued_with(job: BillingJob) do
      account.charge_for(product)
    end

    assert_not account.reload.charged_for?(product)

    perform_enqueued_jobs

    assert account.reload.charged_for?(product)
  end
end

12.3. Testing that Exceptions are Raised

Testing that your job raises an exception in certain cases can be tricky, especially when you have retries configured. The perform_enqueued_jobs helper fails any test where a job raises an exception, so to have the test succeed when the exception is raised you have to call the job's perform method directly.

require "test_helper"

class BillingJobTest < ActiveJob::TestCase
  test "does not charge accounts with insufficient funds" do
    assert_raises(InsufficientFundsError) do
      BillingJob.new(empty_account, product).perform
    end
    assert_not account.reload.charged_for?(product)
  end
end

This method is not recommended in general, as it circumvents some parts of the framework, such as argument serialization.

13. Testing Action Cable

Since Action Cable is used at different levels inside your application, you'll need to test both the channels, connection classes themselves, and that other entities broadcast correct messages.

13.1. Connection Test Case

By default, when you generate a new Rails application with Action Cable, a test for the base connection class (ApplicationCable::Connection) is generated as well under test/channels/application_cable directory.

Connection tests aim to check whether a connection's identifiers get assigned properly or that any improper connection requests are rejected. Here is an example:

class ApplicationCable::ConnectionTest < ActionCable::Connection::TestCase
  test "connects with params" do
    # Simulate a connection opening by calling the `connect` method
    connect params: { user_id: 42 }

    # You can access the Connection object via `connection` in tests
    assert_equal connection.user_id, "42"
  end

  test "rejects connection without params" do
    # Use `assert_reject_connection` matcher to verify that
    # connection is rejected
    assert_reject_connection { connect }
  end
end

You can also specify request cookies the same way you do in integration tests:

test "connects with cookies" do
  cookies.signed[:user_id] = "42"

  connect

  assert_equal connection.user_id, "42"
end

See the API documentation for ActionCable::Connection::TestCase for more information.

13.2. Channel Test Case

By default, when you generate a channel, an associated test will be generated as well under the test/channels directory. Here's an example test with a chat channel:

require "test_helper"

class ChatChannelTest < ActionCable::Channel::TestCase
  test "subscribes and stream for room" do
    # Simulate a subscription creation by calling `subscribe`
    subscribe room: "15"

    # You can access the Channel object via `subscription` in tests
    assert subscription.confirmed?
    assert_has_stream "chat_15"
  end
end

This test is pretty simple and only asserts that the channel subscribes the connection to a particular stream.

You can also specify the underlying connection identifiers. Here's an example test with a web notifications channel:

require "test_helper"

class WebNotificationsChannelTest < ActionCable::Channel::TestCase
  test "subscribes and stream for user" do
    stub_connection current_user: users(:john)

    subscribe

    assert_has_stream_for users(:john)
  end
end

See the API documentation for ActionCable::Channel::TestCase for more information.

13.3. Custom Assertions And Testing Broadcasts Inside Other Components

Action Cable ships with a bunch of custom assertions that can be used to lessen the verbosity of tests. For a full list of available assertions, see the API documentation for ActionCable::TestHelper.

It's a good practice to ensure that the correct message has been broadcasted inside other components (e.g. inside your controllers). This is precisely where the custom assertions provided by Action Cable are pretty useful. For instance, within a model:

require "test_helper"

class ProductTest < ActionCable::TestCase
  test "broadcast status after charge" do
    assert_broadcast_on("products:#{product.id}", type: "charged") do
      product.charge(account)
    end
  end
end

If you want to test the broadcasting made with Channel.broadcast_to, you should use Channel.broadcasting_for to generate an underlying stream name:

# app/jobs/chat_relay_job.rb
class ChatRelayJob < ApplicationJob
  def perform(room, message)
    ChatChannel.broadcast_to room, text: message
  end
end

# test/jobs/chat_relay_job_test.rb
require "test_helper"

class ChatRelayJobTest < ActiveJob::TestCase
  include ActionCable::TestHelper

  test "broadcast message to room" do
    room = rooms(:all)

    assert_broadcast_on(ChatChannel.broadcasting_for(room), text: "Hi!") do
      ChatRelayJob.perform_now(room, "Hi!")
    end
  end
end

14. Running tests in Continuous Integration (CI)

Continuous Integration (CI) is a development practice where changes are frequently integrated into the main codebase, and as such, are automatically tested before merge.

To run all tests in a CI environment, there's just one command you need:

$ bin/rails test

If you are using System Tests, bin/rails test will not run them, since they can be slow. To also run them, add another CI step that runs bin/rails test:system, or change your first step to bin/rails test:all, which runs all tests including system tests.

15. Parallel Testing

Running tests in parallel reduces the time it takes your entire test suite to run. While forking processes is the default method, threading is supported as well.

15.1. Parallel Testing with Processes

The default parallelization method is to fork processes using Ruby's DRb system. The processes are forked based on the number of workers provided. The default number is the actual core count on the machine, but can be changed by the number passed to the parallelize method.

To enable parallelization add the following to your test_helper.rb:

class ActiveSupport::TestCase
  parallelize(workers: 2)
end

The number of workers passed is the number of times the process will be forked. You may want to parallelize your local test suite differently from your CI, so an environment variable is provided to be able to easily change the number of workers a test run should use:

$ PARALLEL_WORKERS=15 bin/rails test

When parallelizing tests, Active Record automatically handles creating a database and loading the schema into the database for each process. The databases will be suffixed with the number corresponding to the worker. For example, if you have 2 workers the tests will create test-database-0 and test-database-1 respectively.

If the number of workers passed is 1 or fewer the processes will not be forked and the tests will not be parallelized and they will use the original test-database database.

Two hooks are provided, one runs when the process is forked, and one runs before the forked process is closed. These can be useful if your app uses multiple databases or performs other tasks that depend on the number of workers.

The parallelize_setup method is called right after the processes are forked. The parallelize_teardown method is called right before the processes are closed.

class ActiveSupport::TestCase
  parallelize_setup do |worker|
    # setup databases
  end

  parallelize_teardown do |worker|
    # cleanup databases
  end

  parallelize(workers: :number_of_processors)
end

These methods are not needed or available when using parallel testing with threads.

15.2. Parallel Testing with Threads

If you prefer using threads or are using JRuby, a threaded parallelization option is provided. The threaded parallelizer is backed by minitest's Parallel::Executor.

To change the parallelization method to use threads over forks put the following in your test_helper.rb:

class ActiveSupport::TestCase
  parallelize(workers: :number_of_processors, with: :threads)
end

Rails applications generated from JRuby or TruffleRuby will automatically include the with: :threads option.

15.3. Testing Parallel Transactions

When you want to test code that runs parallel database transactions in threads, those can block each other because they are already nested under the implicit test transaction.

To workaround this, you can disable transactions in a test case class by setting self.use_transactional_tests = false:

class WorkerTest < ActiveSupport::TestCase
  self.use_transactional_tests = false

  test "parallel transactions" do
    # start some threads that create transactions
  end
end

15.4. Threshold to Parallelize tests

Running tests in parallel adds an overhead in terms of database setup and fixture loading. Because of this, Rails won't parallelize executions that involve fewer than 50 tests.

You can configure this threshold in your test.rb:

config.active_support.test_parallelization_threshold = 100

And also when setting up parallelization at the test case level:

class ActiveSupport::TestCase
  parallelize threshold: 100
end

16. Testing Eager Loading

Normally, applications do not eager load in the development or test environments to speed things up. But they do in the production environment.

If some file in the project cannot be loaded for whatever reason, it is important to detect it before deploying to production.

16.1. Continuous Integration

If your project has CI in place, eager loading in CI is an easy way to ensure the application eager loads.

CIs typically set an environment variable to indicate the test suite is running there. For example, it could be CI:

# config/environments/test.rb
config.eager_load = ENV["CI"].present?

Starting with Rails 7, newly generated applications are configured that way by default.

If your project does not have continuous integration, you can still eager load in the test suite by calling Rails.application.eager_load!:

require "test_helper"

class ZeitwerkComplianceTest < ActiveSupport::TestCase
  test "eager loads all files without errors" do
    assert_nothing_raised { Rails.application.eager_load! }
  end
end

17. Additional Testing Resources

17.1. Errors

In system tests, integration tests and functional controller tests, Rails will attempt to rescue from errors raised and respond with HTML error pages by default. This behavior can be controlled by the config.action_dispatch.show_exceptions configuration.

17.2. Testing Time-Dependent Code

Rails provides built-in helper methods that enable you to assert that your time-sensitive code works as expected.

The following example uses the travel_to helper:

# Given a user is eligible for gifting a month after they register.
user = User.create(name: "Gaurish", activation_date: Date.new(2004, 10, 24))
assert_not user.applicable_for_gifting?

travel_to Date.new(2004, 11, 24) do
  # Inside the `travel_to` block `Date.current` is stubbed
  assert_equal Date.new(2004, 10, 24), user.activation_date
  assert user.applicable_for_gifting?
end

# The change was visible only inside the `travel_to` block.
assert_equal Date.new(2004, 10, 24), user.activation_date

Please see ActiveSupport::Testing::TimeHelpers API reference for more information about the available time helpers.