Guides.rubyonrails.org

Chapters

1. Why Write Tests for your Rails Applications?
2. Introduction to Testing
   • The Test Environment
   • Rails Sets up for Testing from the Word Go
   • The Low-Down on Fixtures
3. Unit Testing your Models
   • Maintaining the test database schema
   • Running Tests
   • What to Include in Your Unit Tests
   • Available Assertions
   • Rails Specific Assertions
4. Functional Tests for Your Controllers
   • What to Include in your Functional Tests
   • Available Request Types for Functional Tests
   • The Four Hashes of the Apocalypse
   • Instance Variables Available
   • Setting Headers and CGI variables
   • Testing Templates and Layouts
   • A Fuller Functional Test Example
   • Testing Views
5. Integration Testing
   • Helpers Available for Integration Tests
   • Integration Testing Examples
6. Rake Tasks for Running your Tests
7. Brief Note About MiniTest
8. Setup and Teardown
9. Testing Routes
10. Testing Your Mailers
    • Keeping the Postman in Check
    • Unit Testing
    • Functional Testing
11. Testing helpers
12. Other Testing Approaches

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. Tests can mangle test data with confidence, that won't touch the data in the development or production databases.

2.2 Rails Sets up for Testing from the Word Go

Rails creates a test folder for you as soon as you create a Rails project using rails new application_name. If you list the contents of this folder 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.

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

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.

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 very 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 space. You can place comments in a fixture file by using the # character in the first column. Keys which resemble YAML keywords such as 'yes' and 'no' are quoted so that the YAML Parser correctly interprets them.

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
about:
  name: About

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

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 folder for your models and controllers test. Loading involves three steps:

• Remove any existing data from the table corresponding to the fixture
• Load the fixture data into the table
• Dump the fixture data into a variable in case you want to access it directly

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 setup as a local variable of 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

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

3 Unit Testing your Models

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

For this guide we will be using Rails scaffolding. It will create the model, a migration, controller and views for the new resource in a single operation. It will also create a full test suite following Rails best practices. I will be using examples from this generated code and will be supplementing it with additional examples where necessary.

When you use rails generate scaffold, for a resource among other things it creates a test stub in the test/models folder:

$ bin/rails generate scaffold post title:string body:text
...
create  app/models/post.rb
create  test/models/post_test.rb
create  test/fixtures/posts.yml
...

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

require 'test_helper'

class PostTest < 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'

As you know by now, test_helper.rb specifies the default configuration to run our tests. This is included with all the tests, so any methods added to this file are available to all your tests.

class PostTest < ActiveSupport::TestCase

The PostTest class defines a test case because it inherits from ActiveSupport::TestCase. PostTest thus has all the methods available from ActiveSupport::TestCase. You'll see those methods a little later in this guide.

Any method defined within a class inherited from MiniTest::Unit::TestCase (which is the superclass of ActiveSupport::TestCase) that begins with test (case sensitive) is simply called a test. So, test_password, test_valid_password and testValidPassword all are legal test names and are run automatically when the test case is run.

Rails 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,

test "the truth" do
  assert true
end

acts as if you had written

def test_the_truth
  assert true
end

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

assert true

This line of code is called an assertion. 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 contains one or more assertions. 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.

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/post_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

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/post_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

This will run all test methods from the test case. Note that test_helper.rb is in the test directory, hence this directory needs to be added to the load path using the -I switch.

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.

To see how a test failure is reported, you can add a failing test to the post_test.rb test case.

test "should not save post without title" do
  post = Post.new
  assert_not post.save
end

Let us run this newly added test.

$ bin/rake test test/models/post_test.rb test_should_not_save_post_without_title
F

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

  1) Failure:
test_should_not_save_post_without_title(PostTest) [test/models/post_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 post without title" do
  post = Post.new
  assert_not post.save, "Saved the post without a title"
end

Running this test shows the friendlier assertion message:

  1) Failure:
test_should_not_save_post_without_title(PostTest) [test/models/post_test.rb:6]:
Saved the post without a title

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

class Post < ActiveRecord::Base
  validates :title, presence: true
end

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

$ bin/rake test test/models/post_test.rb test_should_not_save_post_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).

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/rake test test/models/post_test.rb test_should_report_error
E

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

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

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

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

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/post_test.rb

3.3 What to Include in Your Unit Tests

Ideally, you would like to include a test for everything which could possibly break. It's a good practice to have at least one test for each of your validations and at least one test for every method in your model.

3.4 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. 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. It's not required.

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.

3.5 Rails Specific Assertions

Rails adds some custom assertions of its own to the test/unit framework:

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

4 Functional Tests for Your Controllers

In Rails, testing the various actions of a single controller is called writing functional tests for that controller. Controllers handle the incoming web requests to your application and eventually respond with a rendered 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 Post resource, it has already created the controller code and tests. You can take look at the file posts_controller_test.rb in the test/controllers directory.

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

class PostsControllerTest < ActionController::TestCase
  test "should get index" do
    get :index
    assert_response :success
    assert_not_nil assigns(:posts)
  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 it assigns a valid posts 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.
• An optional hash of request parameters to pass into the action (eg. query string parameters or post variables).
• An optional hash of session variables to pass along with the request.
• An optional hash of flash values.

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, {'id' => "12"}, {'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, {'id' => '12'}, nil, {'message' => 'booya!'})

Let us modify test_should_create_post test in posts_controller_test.rb so that all our test pass:

test "should create post" do
  assert_difference('Post.count') do
    post :create, post: {title: 'Some title'}
  end

  assert_redirected_to post_path(assigns(:post))
end

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 are methods that you can use, however, you'll probably end up using the first two more often than the others.

4.3 The Four Hashes of the Apocalypse

After a request has been made using one of the 6 methods (get, post, etc.) 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)

4.4 Instance Variables Available

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

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

4.5 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

4.6 Testing Templates and Layouts

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"
end

Note that you cannot test for template and layout at the same time, with one call to assert_template method. Also, for the layout test, you can give a regular expression instead of a string, but using the string, makes things clearer. On the other hand, you have to 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.

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

Hence:

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

is the correct way to assert for the layout when the view renders a partial with name _form. Omitting the :partial key in your assert_template call will complain.

4.7 A Fuller Functional Test Example

Here's another example that uses flash, assert_redirected_to, and assert_difference:

test "should create post" do
  assert_difference('Post.count') do
    post :create, post: {title: 'Hi', body: 'This is my first post.'}
  end
  assert_redirected_to post_path(assigns(:post))
  assert_equal 'Post was successfully created.', flash[:notice]
end

4.8 Testing Views

Testing the response to your request by asserting the presence of key HTML elements and their content is a useful way to test the views of your application. The assert_select assertion allows you to do this 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), an expression with substitution values, or an HTML::Selector object.

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 HTML::Node) 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. In this case the inner assert_select runs the assertion on the complete collection of elements selected by the outer assert_select block:

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

Alternatively the collection of elements selected by the outer assert_select may be iterated through so that assert_select may be called separately for each element. Suppose for example that the response contains two ordered lists, each with four list elements then the following tests will both pass.

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

assert_select "ol" do
  assert_select "li", 8
end

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

4.8.1 Additional View-Based Assertions

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

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.'
end

5 Integration Testing

Integration tests are used to test the interaction among any number of controllers. They are generally used to test important work flows within your application.

Unlike Unit and Functional tests, integration tests have to be explicitly created under the 'test/integration' folder within 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
end

Integration tests inherit from ActionDispatch::IntegrationTest. This makes available some additional helpers to use in your integration tests. Also you need to explicitly include the fixtures to be made available to the test.

5.1 Helpers Available for Integration Tests

In addition to the standard testing helpers, there are some additional helpers available to integration tests:

5.2 Integration Testing Examples

A simple integration test that exercises multiple controllers:

require 'test_helper'

class UserFlowsTest < ActionDispatch::IntegrationTest
  test "login and browse site" do
    # login via https
    https!
    get "/login"
    assert_response :success

    post_via_redirect "/login", username: users(:david).username, password: users(:david).password
    assert_equal '/welcome', path
    assert_equal 'Welcome david!', flash[:notice]

    https!(false)
    get "/posts/all"
    assert_response :success
    assert assigns(:posts)
  end
end

As you can see the integration test involves multiple controllers and exercises the entire stack from database to dispatcher. In addition you can have multiple session instances open simultaneously in a test and extend those instances with assertion methods to create a very powerful testing DSL (domain-specific language) just for your application.

Here's an example of multiple sessions and custom DSL in an integration test

require 'test_helper'

class UserFlowsTest < ActionDispatch::IntegrationTest
  test "login and browse site" do
    # User david logs in
    david = login(:david)
    # User guest logs in
    guest = login(:guest)

    # Both are now available in different sessions
    assert_equal 'Welcome david!', david.flash[:notice]
    assert_equal 'Welcome guest!', guest.flash[:notice]

    # User david can browse site
    david.browses_site
    # User guest can browse site as well
    guest.browses_site

    # Continue with other assertions
  end

  private

    module CustomDsl
      def browses_site
        get "/products/all"
        assert_response :success
        assert assigns(:products)
      end
    end

    def login(user)
      open_session do |sess|
        sess.extend(CustomDsl)
        u = users(user)
        sess.https!
        sess.post "/login", username: u.username, password: u.password
        assert_equal '/welcome', sess.path
        sess.https!(false)
      end
    end
end

6 Rake Tasks for Running your Tests

You don't need to set up and run your tests by hand on a test-by-test basis. Rails comes with a number of commands to help in testing. The table below lists all commands that come along in the default Rakefile when you initiate a Rails project.

7 Brief Note About MiniTest

Ruby ships with a boat load of libraries. Ruby 1.8 provides Test::Unit, a framework for unit testing in Ruby. All the basic assertions discussed above are actually defined in Test::Unit::Assertions. The class ActiveSupport::TestCase which we have been using in our unit and functional tests extends Test::Unit::TestCase, allowing us to use all of the basic assertions in our tests.

Ruby 1.9 introduced MiniTest, an updated version of Test::Unit which provides a backwards compatible API for Test::Unit. You could also use MiniTest in Ruby 1.8 by installing the minitest gem.

8 Setup and Teardown

If you would like to run a block of code before the start of each test and another block of code after the end of each test you have two special callbacks for your rescue. Let's take note of this by looking at an example for our functional test in Posts controller:

require 'test_helper'

class PostsControllerTest < ActionController::TestCase

  # called before every single test
  def setup
    @post = posts(:one)
  end

  # called after every single test
  def teardown
    # as we are re-initializing @post before every test
    # setting it to nil here is not essential but I hope
    # you understand how you can use the teardown method
    @post = nil
  end

  test "should show post" do
    get :show, id: @post.id
    assert_response :success
  end

  test "should destroy post" do
    assert_difference('Post.count', -1) do
      delete :destroy, id: @post.id
    end

    assert_redirected_to posts_path
  end

end

Above, the setup method is called before each test and so @post is available for each of the tests. Rails implements setup and teardown as ActiveSupport::Callbacks. Which essentially means you need not only use setup and teardown as methods in your tests. You could specify them by using:

• a block
• a method (like in the earlier example)
• a method name as a symbol
• a lambda

Let's see the earlier example by specifying setup callback by specifying a method name as a symbol:

require 'test_helper'

class PostsControllerTest < ActionController::TestCase

  # called before every single test
  setup :initialize_post

  # called after every single test
  def teardown
    @post = nil
  end

  test "should show post" do
    get :show, id: @post.id
    assert_response :success
  end

  test "should update post" do
    patch :update, id: @post.id, post: {}
    assert_redirected_to post_path(assigns(:post))
  end

  test "should destroy post" do
    assert_difference('Post.count', -1) do
      delete :destroy, id: @post.id
    end

    assert_redirected_to posts_path
  end

  private

    def initialize_post
      @post = posts(:one)
    end
end

9 Testing Routes

Like everything else in your Rails application, it is recommended that you test your routes. An example test for a route in the default show action of Posts controller above should look like:

test "should route to post" do
  assert_routing '/posts/1', {controller: "posts", action: "show", id: "1"}
end

10 Testing Your Mailers

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

10.1 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

10.1.1 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.

10.2 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.

10.2.1 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.

10.2.2 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
    email = UserMailer.create_invite('me@example.com',
                                     'friend@example.com', Time.now).deliver
    assert_not ActionMailer::Base.deliveries.empty?

    # 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 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.

Cheers!

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).

10.3 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, email: 'friend@example.com'
    end
    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)
  end
end

11 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. Rails provides a generator which generates both the helper and the test file:

$ bin/rails generate helper User
      create  app/helpers/user_helper.rb
      invoke  test_unit
      create    test/helpers/user_helper_test.rb

The generated test file contains the following code:

require 'test_helper'

class UserHelperTest < ActionView::TestCase
end

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
    # ...
  end
end

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

12 Other Testing Approaches

The built-in test/unit 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.
• Machinist, another 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

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