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A Guide to Testing Rails Applications

This guide covers built-in mechanisms in Rails for testing your application.

After reading this guide, you will know:

1 Why Write Tests for your Rails Applications?

Rails makes it super easy to write your tests. It starts by producing skeleton test code while you are creating your models and controllers.

By simply running your Rails tests you can ensure your code adheres to the desired functionality even after some major code refactoring.

Rails tests can also simulate browser requests and thus you can test your application's response without having to test it through your browser.

2 Introduction to Testing

Testing support was woven into the Rails fabric from the beginning. It wasn't an "oh! let's bolt on support for running tests because they're new and cool" epiphany. Just about every Rails application interacts heavily with a database and, as a result, your tests will need a database to interact with as well. To write efficient tests, you'll need to understand how to set up this database and populate it with sample data.

2.1 The Test Environment

By default, 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 mangle test data with confidence, without worrying about the data in the development or production databases.

Also, 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.

2.2 Rails Sets up for Testing from the Word Go

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

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

The models directory is meant to hold tests for your models, the controllers directory is meant to hold tests for your controllers and the integration directory is meant to hold tests that involve any number of controllers interacting. There is also a directory for testing your mailers and one for testing view helpers.

Fixtures are a way of organizing test data; they reside in the fixtures directory.

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

2.3 The Low-Down on 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.

2.3.1 What Are Fixtures?

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

You'll find fixtures under your test/fixtures directory. When you run rails generate model to create a new model fixture stubs will be automatically created and placed in this directory.

2.3.2 YAML

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!
  name: David Heinemeier Hansson
  birthday: 1979-10-15
  profession: Systems development

  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 space. You can place comments in a fixture file by using the # character in the first column.

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

# In fixtures/categories.yml
  name: About

# In fixtures/articles.yml
  title: Welcome to Rails!
  body: Hello world!
  category: about

Notice the category key of the one article found in fixtures/articles.yml has a value of about. This tells Rails to load the category about found in fixtures/categories.yml.

For associations to reference one another by name, you cannot specify the id: attribute on the associated fixtures. Rails will auto assign a primary key to be consistent between runs. For more information on this association behavior please read the Fixtures API documentation.

2.3.3 ERB'in It Up

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 %>

2.3.4 Fixtures in Action

Rails by default automatically loads all fixtures from the test/fixtures directory for your models and controllers test. 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

In order to remove existing data from the database, Rails tries to disable referential integrity triggers (like foreign keys and check constraints). If you are getting annoying permission errors on running tests, make sure the database user has privilege to disable these triggers in testing environment. (In PostgreSQL, only superusers can disable all triggers. Read more about PostgreSQL permissions here)

2.3.5 Fixtures are Active Record objects

Fixtures are instances of Active Record. As mentioned in point #3 above, you can access the object directly because it is automatically available as a method whose scope is local of the test case. For example:

# this will return the User object for the fixture named david

# this will return the property for david called id

# one can also access methods available on the User class
email(david.girlfriend.email, david.location_tonight)

2.4 Rake Tasks for Running your Tests

Rails comes with a number of built-in rake tasks to help with testing. The table below lists the commands included in the default Rakefile when a Rails project is created.

Tasks Description
rake test Runs all tests in the test directory. You can also run rake and Rails will run all tests by default
rake test:controllers Runs all the controller tests from test/controllers
rake test:functionals Runs all the functional tests from test/controllers, test/mailers, and test/functional
rake test:helpers Runs all the helper tests from test/helpers
rake test:integration Runs all the integration tests from test/integration
rake test:jobs Runs all the job tests from test/jobs
rake test:mailers Runs all the mailer tests from test/mailers
rake test:models Runs all the model tests from test/models
rake test:units Runs all the unit tests from test/models, test/helpers, and test/unit
rake test:db Runs all tests in the test directory and resets the db

We will cover each of types Rails tests listed above in this guide.

3 Unit Testing your Models

In Rails, unit tests are what you write to test your models.

For this guide we will be using the application we built in the Getting Started with Rails guide.

If you remember when you used the rails generate scaffold command from earlier. We created our first resource among other things it created a test stub in the test/models directory:

$ bin/rails generate scaffold article title:string body:text
create  app/models/article.rb
create  test/models/article_test.rb
create  test/fixtures/articles.yml

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

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

require 'test_helper'

By requiring this file, test_helper.rb the default configuration to run our tests is loaded. We will include this with all the tests we write, so any methods added to this file are available to all your tests.

class ArticleTest < ActiveSupport::TestCase

The ArticleTest class defines a test case because it inherits from ActiveSupport::TestCase. ArticleTest thus has all the methods available from ActiveSupport::TestCase. Later in this guide, you'll see some of the methods it gives you.

Any method defined within a class inherited from Minitest::Test (which is the superclass of ActiveSupport::TestCase) that begins with test_ (case sensitive) is simply called a test. So, methods defined as test_password and test_valid_password are legal 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 normal Minitest::Unit test with method names prefixed with test_. So you don't have to worry about naming the methods, and you can write something like:

test "the truth" do
  assert true

Which is approximately the same as writing this:

def test_the_truth
  assert true

However only the test macro allows a more readable test name. You can still use regular method definitions though.

The method name is generated by replacing spaces with underscores. The result does not need to be a valid Ruby identifier though, the name may contain punctuation characters etc. That's because in Ruby technically any string may be a method name. This may require use of define_method and send calls to function properly, but formally there's little restriction on the name.

Next, let's look at our first 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 = 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 must contain at least one assertion, with no restriction as to how many assertions are allowed. Only when all the assertions are successful will the test pass.

3.1 Maintaining the test database schema

In order to run your tests, your test database will need to have the current structure. The test helper checks whether your test database has any pending migrations. If so, 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 against the development database (bin/rake db:migrate) will bring the schema up to date.

If existing migrations required modifications, the test database needs to be rebuilt. This can be done by executing bin/rake db:test:prepare.

3.2 Running Tests

Running a test is as simple as invoking the file containing the test cases through rake test command.

$ bin/rake test test/models/article_test.rb

Finished tests in 0.009262s, 107.9680 tests/s, 107.9680 assertions/s.

1 tests, 1 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 running the test and providing the test method name.

$ bin/rake test test/models/article_test.rb test_the_truth

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

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

The . (dot) above indicates a passing test. When a test fails you see an F; when a test throws an error you see an E in its place. The last line of the output is the summary.

3.2.1 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.

test "should not save article without title" do
  article = Article.new
  assert_not article.save

Let us run this newly added test.

$ bin/rake test test/models/article_test.rb test_should_not_save_article_without_title

Finished tests in 0.044632s, 22.4054 tests/s, 22.4054 assertions/s.

  1) Failure:
test_should_not_save_article_without_title(ArticleTest) [test/models/article_test.rb:6]:
Failed assertion, no message given.

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

In the output, F denotes a failure. You can see the corresponding trace shown under 1) along with the name of the failing test. The next few lines contain the stack trace followed by a message which mentions the actual value and the expected value by the assertion. The default assertion messages provide just enough information to help pinpoint the error. To make the assertion failure message more readable, every assertion provides an optional message parameter, as shown here:

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

Running this test shows the friendlier assertion message:

  1) Failure:
test_should_not_save_article_without_title(ArticleTest) [test/models/article_test.rb:6]:
Saved the article without a title

Now to get this test to pass we can add a model level validation for the title field.

class Article < ActiveRecord::Base
  validates :title, presence: true

Now the test should pass. Let us verify by running the test again:

$ bin/rake test test/models/article_test.rb test_should_not_save_article_without_title

Finished tests in 0.047721s, 20.9551 tests/s, 20.9551 assertions/s.

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

Now, if you noticed, we first wrote a test which fails for a desired functionality, then we wrote some code which adds the functionality and finally we ensured that our test passes. This approach to software development is referred to as Test-Driven Development (TDD).

3.2.2 What an error looks like

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
  assert true

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

$ bin/rake test test/models/article_test.rb test_should_report_error

Finished tests in 0.030974s, 32.2851 tests/s, 0.0000 assertions/s.

  1) Error:
NameError: undefined local variable or method `some_undefined_variable' for #<ArticleTest:0x007fe32e24afe0>
    test/models/article_test.rb:10:in `block in <class:ArticleTest>'

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

Notice the 'E' in the output. It denotes a test with error.

The execution of each test method stops as soon as any error or an assertion failure is encountered, and the test suite continues with the next method. All test methods are executed in random order. The config.active_support.test_order option can be used to configure test order.

When a test fails you are presented with the corresponding backtrace. By default Rails filters that backtrace and will only print lines relevant to your application. This eliminates the framework noise and helps to focus on your code. However there are situations when you want to see the full backtrace. simply set the BACKTRACE environment variable to enable this behavior:

$ BACKTRACE=1 bin/rake test test/models/article_test.rb

If we want this test to pass we can modify it to use assert_raises like so:

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

This test should now pass.

3.3 Available Assertions

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

There are a bunch of different types of assertions you can use that come with Minitest, the default testing library used by Rails.

For a list of all available assertions please check the Minitest API documentation, specifically Minitest::Assertions

Because of the modular nature of the testing framework, it is possible to create your own assertions. In fact, that's exactly what Rails does. It includes some specialized assertions to make your life easier.

Creating your own assertions is an advanced topic that we won't cover in this tutorial.

3.4 Rails Specific Assertions

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

Assertion Purpose
assert_difference(expressions, difference = 1, message = nil) {...} Test numeric difference between the return value of an expression as a result of what is evaluated in the yielded block.
assert_no_difference(expressions, message = nil, &amp;block) Asserts that the numeric result of evaluating an expression is not changed before and after invoking the passed in block.
assert_recognizes(expected_options, path, extras={}, message=nil) Asserts that the routing of the given path was handled correctly and that the parsed options (given in the expected_options hash) match path. Basically, it asserts that Rails recognizes the route given by expected_options.
assert_generates(expected_path, options, defaults={}, extras = {}, message=nil) Asserts that the provided options can be used to generate the provided path. This is the inverse of assert_recognizes. The extras parameter is used to tell the request the names and values of additional request parameters that would be in a query string. The message parameter allows you to specify a custom error message for assertion failures.
assert_response(type, message = nil) Asserts that the response comes with a specific status code. You can specify :success to indicate 200-299, :redirect to indicate 300-399, :missing to indicate 404, or :error to match the 500-599 range. You can also pass an explicit status number or its symbolic equivalent. For more information, see full list of status codes and how their mapping works.
assert_redirected_to(options = {}, message=nil) Assert that the redirection options passed in match those of the redirect called in the latest action. This match can be partial, such that assert_redirected_to(controller: "weblog") will also match the redirection of redirect_to(controller: "weblog", action: "show") and so on. You can also pass named routes such as assert_redirected_to root_path and Active Record objects such as assert_redirected_to @article.
assert_template(expected = nil, message=nil) Asserts that the request was rendered with the appropriate template file.

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

3.5 A Brief Note About Minitest

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
  • ActionController::TestCase
  • ActionMailer::TestCase
  • ActionView::TestCase
  • ActionDispatch::IntegrationTest
  • ActiveJob::TestCase

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

For more information on Minitest, refer to Minitest

4 Functional Tests for Your Controllers

In Rails, testing the various actions of a controller is a form of writing functional tests. Remember your controllers handle the incoming web requests to your application and eventually respond with a rendered view. When writing functional tests, you're testing how your actions handle the requests and the expected result, or response in some cases an HTML view.

4.1 What to Include in your Functional Tests

You should 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 object stored in the response template?
  • was the appropriate message displayed to the user in the view?

Now that we have used Rails scaffold generator for our Article resource, it has already created the controller code and tests. You can take look at the file articles_controller_test.rb in the test/controllers directory.

Let me take you through one such test, test_should_get_index from the file articles_controller_test.rb.

class ArticlesControllerTest < ActionController::TestCase
  test "should get index" do
    get :index
    assert_response :success
    assert_not_nil assigns(:articles)

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 it assigns a valid articles instance variable.

The get method kicks off the web request and populates the results into the response. It accepts 4 arguments:

  • The action of the controller you are requesting. This can be in the form of a string or a symbol.

  • params: option with a hash of request parameters to pass into the action (e.g. query string parameters or article variables).

  • session: option with a hash of session variables to pass along with the request.

  • flash: option with a hash of flash values.

All the keyword arguments are optional.

Example: Calling the :show action, passing an id of 12 as the params and setting a user_id of 5 in the session:

get(:show, params: { 'id' => "12" }, session: { 'user_id' => 5 })

Another example: Calling the :view action, passing an id of 12 as the params, this time with no session, but with a flash message.

get(:view, params: { 'id' => '12' }, flash: { 'message' => 'booya!' })

If you try running test_should_create_article test from articles_controller_test.rb it will fail on account of the newly added model level validation and rightly so.

Let us modify test_should_create_article test in articles_controller_test.rb so that all our test pass:

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

  assert_redirected_to article_path(assigns(:article))

Now you can try running all the tests and they should pass.

4.2 Available 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 request types have equivalent methods that you can use. In a typical C.R.U.D. application you'll be using get, post, put and delete more often.

Functional tests do not verify whether the specified request type is accepted by the action, we're more concerned with the result. Request tests exist for this use case to make your tests more purposeful.

4.3 Testing XHR (AJAX) requests

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

test "ajax request responds with no layout" do
  get :show, params: { id: articles(:first).id }, xhr: true

  assert_template :index
  assert_template layout: nil

4.4 The Four Hashes of the Apocalypse

After a request has been made and processed, you will have 4 Hash objects ready for use:

  • assigns - Any objects that are stored as instance variables in actions for use in views.
  • 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, except for assigns. For example:

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

# Because you can't use assigns[:something] for historical reasons:
assigns["something"]          assigns(:something)

4.5 Instance Variables Available

You also have access to three instance variables in your functional tests:

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

4.6 Setting Headers and CGI variables

HTTP headers and CGI variables can be set directly on the @request instance variable:

# setting a HTTP Header
@request.headers["Accept"] = "text/plain, text/html"
get :index # simulate the request with custom header

# setting a CGI variable
@request.headers["HTTP_REFERER"] = "http://example.com/home"
post :create # simulate the request with custom env variable

4.7 Testing Templates and Layouts

Eventually, you may want to test whether a specific layout is rendered in the view of a response.

4.7.1 Asserting Templates

If you want to make sure that the response rendered the correct template and layout, you can use the assert_template method:

test "index should render correct template and layout" do
  get :index
  assert_template :index
  assert_template layout: "layouts/application"

  # You can also pass a regular expression.
  assert_template layout: /layouts\/application/

You cannot test for template and layout at the same time, with a single call to assert_template.

You must include the "layouts" directory name even if you save your layout file in this standard layout directory. Hence, assert_template layout: "application" will not work.

4.7.2 Asserting Partials

If your view renders any partial, when asserting for the layout, you can to assert for the partial at the same time. Otherwise, assertion will fail.

Remember, we added the "_form" partial to our creating Articles view? Let's write an assertion for that in the :new action now:

test "new should render correct layout" do
  get :new
  assert_template layout: "layouts/application", partial: "_form"

This is the correct way to assert for when the view renders a partial with a given name. As identified by the :partial key passed to the assert_template call.

4.8 Testing flash notices

If you remember from earlier one of the Four Hashes of the Apocalypse was flash.

We want to add a flash message to our blog application whenever someone successfully creates a new Article.

Let's start by adding this assertion to our test_should_create_article test:

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

  assert_redirected_to article_path(assigns(:article))
  assert_equal 'Article was successfully created.', flash[:notice]

If we run our test now, we should see a failure:

$ bin/rake test test/controllers/articles_controller_test.rb test_should_create_article
Run options: -n test_should_create_article --seed 32266

# Running:


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

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

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

Let's implement the flash message now in our controller. Our :create action should now look like this:

def create
  @article = Article.new(article_params)

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

Now if we run our tests, we should see it pass:

$ bin/rake test test/controllers/articles_controller_test.rb test_should_create_article
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

4.9 Putting it together

At this point our Articles controller tests the :index as well as :new and :create actions. What about dealing with existing data?

Let's write a test for the :show action:

test "should show article" do
  article = articles(:one)
  get :show, params: { id: article.id }
  assert_response :success

Remember from our discussion earlier on fixtures the articles() method will give us access to our Articles fixtures.

How about deleting an existing Article?

test "should destroy article" do
  article = articles(:one)
  assert_difference('Article.count', -1) do
    delete :destroy, params: { id: article.id }

  assert_redirected_to articles_path

We can also add a test for updating an existing Article.

test "should update article" do
  article = articles(:one)
  patch :update, params: { id: article.id, article: { title: "updated" } }
  assert_redirected_to article_path(assigns(:article))

Notice we're starting to see some duplication in these three tests, they both access the same Article fixture data. We can D.R.Y. this up by using the setup and teardown methods provided by ActiveSupport::Callbacks.

Our test should now look something like this, disregard the other tests we're leaving them out for brevity.

require 'test_helper'

class ArticlesControllerTest < ActionController::TestCase
  # called before every single test
  def setup
    @article = articles(:one)

  # called after every single test
  def teardown
    # when controller is using cache it may be a good idea to reset it afterwards

  test "should show article" do
    # Reuse the @article instance variable from setup
    get :show, params: { id: @article.id }
    assert_response :success

  test "should destroy article" do
    assert_difference('Article.count', -1) do
      delete :destroy, params: { id: @article.id }

    assert_redirected_to articles_path

  test "should update article" do
    patch :update, params: { id: @article.id, article: { title: "updated" } }
    assert_redirected_to article_path(assigns(:article))

Similar to other callbacks in Rails, the setup and teardown methods can also be used by passing a block, lambda, or method name as a symbol to call.

4.10 Test helpers

To avoid code duplication, you can add your own test helpers. Sign in helper can be a good example:


module SignInHelper
  def sign_in(user)
    session[:user_id] = user.id

class ActionController::TestCase
  include SignInHelper

require 'test_helper'

class ProfileControllerTest < ActionController::TestCase

  test "should show profile" do
    # helper is now reusable from any controller test case
    sign_in users(:david)

    get :show
    assert_response :success
    assert_equal users(:david), assigns(:user)

5 Testing Routes

Like everything else in your Rails application, it is recommended that you test your routes. Below are example tests for the routes of default show and create action of Articles controller above and it should look like:

class ArticleRoutesTest < ActionController::TestCase
  test "should route to article" do
    assert_routing '/articles/1', { controller: "articles", action: "show", id: "1" }

  test "should route to create article" do
    assert_routing({ method: 'post', path: '/articles' }, { controller: "articles", action: "create" })

I've added this file here test/controllers/articles_routes_test.rb and if we run the test we should see:

$ bin/rake test test/controllers/articles_routes_test.rb

# Running:


Finished in 0.069381s, 28.8263 runs/s, 86.4790 assertions/s.

2 runs, 6 assertions, 0 failures, 0 errors, 0 skips

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

6 Testing Views

Testing the response to your request by asserting the presence of key HTML elements and their content is a common way to test the views of your application. The assert_select method allows you to query HTML elements of the response by using a simple yet powerful syntax.

There are two forms of assert_select:

assert_select(selector, [equality], [message]) ensures that the equality condition is met on the selected elements through the selector. The selector may be a CSS selector expression (String) or an expression with substitution values.

assert_select(element, selector, [equality], [message]) ensures that the equality condition is met on all the selected elements through the selector starting from the element (instance of Nokogiri::XML::Node or Nokogiri::XML::NodeSet) and its descendants.

For example, you could verify the contents on the title element in your response with:

assert_select 'title', "Welcome to Rails Testing Guide"

You can also use nested assert_select blocks for deeper investigation.

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

assert_select 'ul.navigation' do
  assert_select 'li.menu_item'

A collection of selected elements may be iterated through so that assert_select 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_select "ol" do |elements|
  elements.each do |element|
    assert_select element, "li", 4

assert_select "ol" do
  assert_select "li", 8

This assertion is quite powerful. For more advanced usage, refer to its documentation.

6.1 Additional View-Based Assertions

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

Assertion Purpose
assert_select_email Allows you to make assertions on the body of an e-mail.
assert_select_encoded Allows you to make assertions on encoded HTML. It does this by un-encoding the contents of each element and then calling the block with all the un-encoded elements.
css_select(selector) or css_select(element, selector) Returns an array of all the elements selected by the selector. In the second variant it first matches the base element and tries to match the selector expression on any of its children. If there are no matches both variants return an empty array.

Here's an example of using assert_select_email:

assert_select_email do
  assert_select 'small', 'Please click the "Unsubscribe" link if you want to opt-out.'

7 Testing helpers

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.

A helper test looks like so:

require 'test_helper'

class UserHelperTest < ActionView::TestCase

A helper is just a simple module where you can define methods which are available into your views. To test the output of the helper's methods, you just have to use a mixin like this:

class UserHelperTest < ActionView::TestCase
  include UserHelper

  test "should return the user name" do
    # ...

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

8 Integration Testing

Integration tests are used to test how various parts of your application interact. They are generally used to test important work flows within your application.

For creating Rails integration tests, we use the 'test/integration' directory for your application. Rails provides a generator to create an integration test skeleton for you.

$ bin/rails generate integration_test user_flows
      exists  test/integration/
      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

Inheriting from ActionDispatch::IntegrationTest comes with some advantages. This makes available some additional helpers to use in your integration tests.

8.1 Helpers Available for Integration Tests

In addition to the standard testing helpers, inheriting ActionDispatch::IntegrationTest comes with some additional helpers available when writing integration tests. Let's briefly introduce you to the three categories of helpers you get to choose from.

For dealing with the integration test runner, see ActionDispatch::Integration::Runner.

When performing requests, you will have ActionDispatch::Integration::RequestHelpers available for your use.

If you'd like to modify the session, or state of your integration test you should look for ActionDispatch::Integration::Session to help.

8.2 Implementing an integration test

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

We'll start by generating our integration test skeleton:

$ bin/rails generate integration_test blog_flow

It should have created a test file placeholder for us, with the output of the previous command you should see:

      invoke  test_unit
      create    test/integration/blog_flow_test.rb

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

require 'test_helper'

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

If you remember from earlier in the "Testing Views" section we covered assert_select to query the resulting HTML of a request.

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

8.2.1 Creating articles integration

How about testing our ability to create a new article in our blog and see the resulting article.

test "can create an article" do
  get "/articles/new"
  assert_response :success
  assert_template "articles/new", partial: "articles/_form"

  post "/articles",
    params: { article: { title: "can create", body: "article successfully." } }
  assert_response :redirect
  assert_response :success
  assert_template "articles/show"
  assert_select "p", "Title:\n  can create"

Let's break this test down so we can understand it.

We start by calling the :new action on our Articles controller. This response should be successful, and we can verify the correct template is rendered including the form partial.

After this we make a post request to the :create action of our Articles controller:

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

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

Don't forget to call follow_redirect! if you plan to make subsequent requests after a redirect is made.

Finally we can assert that our response was successful, template was rendered, and our new article is readable on the page.

8.2.2 Taking it further

We were able to successfully test a very small workflow for visiting our blog and creating a new article. If we wanted to take this further we could add tests for commenting, removing articles, or editting comments. Integration tests are a great place to experiment with all kinds of use-cases for our applications.

9 Testing Your Mailers

Testing mailer classes requires some specific tools to do a thorough job.

9.1 Keeping the Postman in Check

Your mailer classes - like every other part of your Rails application - should be tested to ensure that it is 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
9.1.1 From All Sides

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 minute details produced by the mailer; instead, we test that our 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.

9.2 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.

9.2.1 Revenge of the 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.

When you generated your mailer, the generator creates stub fixtures for each of the mailers actions. If you didn't use the generator you'll have to make those files yourself.

9.2.2 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. It is an adapted version of the base test created by the generator for an invite action.

require 'test_helper'

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Send the email, then test that it got queued
    assert_emails 1 do
      email = UserMailer.create_invite('me@example.com',
                                       'friend@example.com', Time.now).deliver_now

    # 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

In the test we send the email and store the returned object in the email variable. We then ensure that it was sent (the first assert), then, in the second batch of assertions, we ensure that the email does indeed contain what we expect. 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.


This is the right time to understand a little more about writing tests for your mailers. The line ActionMailer::Base.delivery_method = :test in config/environments/test.rb sets the delivery method to test mode so that email will not actually be delivered (useful to avoid spamming your users while testing) but instead it will be appended to an array (ActionMailer::Base.deliveries).

The ActionMailer::Base.deliveries array is only reset automatically in ActionMailer::TestCase tests. If you want to have a clean slate outside Action Mailer tests, you can reset it manually with: ActionMailer::Base.deliveries.clear

9.3 Functional Testing

Functional testing for mailers involves more than just checking that the email body, recipients and so forth are correct. In functional mail tests you call the mail deliver methods and check that the appropriate emails have been appended to the delivery list. It is fairly safe to assume that the deliver methods themselves do their job. You are probably more interested in whether your own business logic is sending emails when you expect them to go out. For example, you can check that the invite friend operation is sending an email appropriately:

require 'test_helper'

class UserControllerTest < ActionController::TestCase
  test "invite friend" do
    assert_difference 'ActionMailer::Base.deliveries.size', +1 do
      post :invite_friend, params: { email: 'friend@example.com' }
    invite_email = ActionMailer::Base.deliveries.last

    assert_equal "You have been invited by me@example.com", invite_email.subject
    assert_equal 'friend@example.com', invite_email.to[0]
    assert_match(/Hi friend@example.com/, invite_email.body.to_s)

10 Testing Jobs

Since your custom jobs can be queued at different levels inside your application, you'll need to test both jobs themselves (their behavior when they get enqueued) and that other entities correctly enqueue them.

10.1 A Basic Test Case

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

require 'test_helper'

class BillingJobTest < ActiveJob::TestCase
  test 'that account is charged' do
    BillingJob.perform_now(account, product)
    assert account.reload.charged_for?(product)

This test is pretty simple and only asserts that the job get the work done as expected.

By default, ActiveJob::TestCase will set the queue adapter to :test so that your jobs are performed inline. It will also ensure that all previously performed and enqueued jobs are cleared before any test run so you can safely assume that no jobs have already been executed in the scope of each test.

10.2 Custom Assertions And Testing Jobs Inside Other Components

Active Job 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 ActiveJob::TestHelper.

It's a good practice to ensure that your jobs correctly get enqueued or performed wherever you invoke them (e.g. inside your controllers). This is precisely where the custom assertions provided by Active Job are pretty useful. For instance, within a model:

require 'test_helper'

class ProductTest < ActiveJob::TestCase
  test 'billing job scheduling' do
    assert_enqueued_with(job: BillingJob) do

11 Other Testing Approaches

The built-in minitest based testing is not the only way to test Rails applications. Rails developers have come up with a wide variety of other approaches and aids for testing, including:

  • NullDB, a way to speed up testing by avoiding database use.
  • Factory Girl, a replacement for fixtures.
  • Fixture Builder, a tool that compiles Ruby factories into fixtures before a test run.
  • MiniTest::Spec Rails, use the MiniTest::Spec DSL within your rails tests.
  • Shoulda, an extension to test/unit with additional helpers, macros, and assertions.
  • RSpec, a behavior-driven development framework
  • Capybara, Acceptance test framework for web applications


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