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Testing Rails Applications
This guide covers built-in mechanisms in Rails for testing your application.
After reading this guide, you will know:
- Rails testing terminology.
- How to write unit, functional, integration, and system tests for your application.
- Other popular testing approaches and plugins.
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 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.
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.
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
application_system_test_case.rb fixtures/ integration/ models/ test_helper.rb
controllers/ helpers/ mailers/ system/
The helpers
, mailers
, and models
directories are meant to hold tests for view helpers, mailers, and models, respectively. The controllers
directory is meant to hold tests for controllers, routes, and views. The integration
directory is meant to hold tests for 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 organizing test data; they reside in the fixtures
directory.
A jobs
directory will also be created when an associated test is first generated.
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.
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
.
NOTE: Your tests are run under RAILS_ENV=test
.
Rails meets Minitest
If you remember, we used the rails generate model
command in the
Getting Started with Rails guide. We created our first
model, and among other things it created test stubs in the test
directory:
$ bin/rails generate model 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
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 our 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, we'll see some of the methods it gives us.
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
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.
NOTE: 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 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.
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
end
Let us run this newly added test (where 6
is the number of line where the test is defined).
$ bin/rails test test/models/article_test.rb:6
Run options: --seed 44656
# Running:
F
Failure:
ArticleTest#test_should_not_save_article_without_title [/path/to/blog/test/models/article_test.rb:6]:
Expected true to be nil or false
bin/rails test test/models/article_test.rb:6
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
denotes a failure. You can see the corresponding trace shown under Failure
along with the name of the failing test. The next few lines contain the stack trace followed by a message that 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"
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
Now to get this test to pass we can add a model level validation for the title field.
class Article < ApplicationRecord
validates :title, presence: true
end
Now the test should pass. Let us verify by running the test again:
$ bin/rails test test/models/article_test.rb:6
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
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).
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
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
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 error.
NOTE: 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. Set the -b
(or --backtrace
) argument to enable this behavior:
$ bin/rails test -b 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
some_undefined_variable
end
end
This test should now pass.
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.
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.
Assertion | Purpose |
---|---|
assert( test, [msg] ) |
Ensures that test is true. |
assert_not( test, [msg] ) |
Ensures that test is false. |
assert_equal( expected, actual, [msg] ) |
Ensures that expected == actual is true. |
assert_not_equal( expected, actual, [msg] ) |
Ensures that expected != actual is true. |
assert_same( expected, actual, [msg] ) |
Ensures that expected.equal?(actual) is true. |
assert_not_same( expected, actual, [msg] ) |
Ensures that expected.equal?(actual) is false. |
assert_nil( obj, [msg] ) |
Ensures that obj.nil? is true. |
assert_not_nil( obj, [msg] ) |
Ensures that obj.nil? is false. |
assert_empty( obj, [msg] ) |
Ensures that obj is empty? . |
assert_not_empty( obj, [msg] ) |
Ensures that obj is not empty? . |
assert_match( regexp, string, [msg] ) |
Ensures that a string matches the regular expression. |
assert_no_match( regexp, string, [msg] ) |
Ensures that a string doesn't match the regular expression. |
assert_includes( collection, obj, [msg] ) |
Ensures that obj is in collection . |
assert_not_includes( collection, obj, [msg] ) |
Ensures that obj is not in collection . |
assert_in_delta( expected, actual, [delta], [msg] ) |
Ensures that the numbers expected and actual are within delta of each other. |
assert_not_in_delta( expected, actual, [delta], [msg] ) |
Ensures that the numbers expected and actual are not within delta of each other. |
assert_in_epsilon ( expected, actual, [epsilon], [msg] ) |
Ensures that the numbers expected and actual have a relative error less than epsilon . |
assert_not_in_epsilon ( expected, actual, [epsilon], [msg] ) |
Ensures that the numbers expected and actual don't have a relative error less than epsilon . |
assert_throws( symbol, [msg] ) { block } |
Ensures that the given block throws the symbol. |
assert_raises( exception1, exception2, ... ) { block } |
Ensures that the given block raises one of the given exceptions. |
assert_instance_of( class, obj, [msg] ) |
Ensures that obj is an instance of class . |
assert_not_instance_of( class, obj, [msg] ) |
Ensures that obj is not an instance of class . |
assert_kind_of( class, obj, [msg] ) |
Ensures that obj is an instance of class or is descending from it. |
assert_not_kind_of( class, obj, [msg] ) |
Ensures that obj is not an instance of class and is not descending from it. |
assert_respond_to( obj, symbol, [msg] ) |
Ensures that obj responds to symbol . |
assert_not_respond_to( obj, symbol, [msg] ) |
Ensures that obj does not respond to symbol . |
assert_operator( obj1, operator, [obj2], [msg] ) |
Ensures that obj1.operator(obj2) is true. |
assert_not_operator( obj1, operator, [obj2], [msg] ) |
Ensures that obj1.operator(obj2) is false. |
assert_predicate ( obj, predicate, [msg] ) |
Ensures that obj.predicate is true, e.g. assert_predicate str, :empty? |
assert_not_predicate ( obj, predicate, [msg] ) |
Ensures that obj.predicate is false, e.g. assert_not_predicate str, :empty? |
flunk( [msg] ) |
Ensures failure. This is useful to explicitly mark a test that isn't finished yet. |
The above are a subset of assertions that minitest supports. For an exhaustive &
more up-to-date list, please check
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.
NOTE: Creating your own assertions is an advanced topic that we won't cover in this tutorial.
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, &block) |
Asserts that the numeric result of evaluating an expression is not changed before and after invoking the passed in block. |
assert_changes(expressions, message = nil, from:, to:, &block) |
Test that the result of evaluating an expression is changed after invoking the passed in block. |
assert_no_changes(expressions, message = nil, &block) |
Test the result of evaluating an expression is not changed after invoking the passed in block. |
assert_nothing_raised { block } |
Ensures that the given block doesn't raise any exceptions. |
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) |
Asserts 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 . |
You'll see the usage of some of these assertions in the next chapter.
A Brief Note About 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::IntegrationTest
ActionDispatch::SystemTestCase
Rails::Generators::TestCase
Each of these classes include Minitest::Assertions
, allowing us to use all of the basic assertions in our tests.
NOTE: For more information on Minitest
, refer to its
documentation.
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 passing the bin/rails test
command the filename containing the test cases.
$ bin/rails test test/models/article_test.rb
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
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 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, deferring test output at the end of test run and so on. Check the documentation of the test runner as follows:
$ bin/rails test -h
Usage: bin/rails test [options] [files or directories]
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 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.
-n, --name PATTERN Filter run on /regexp/ or string.
--exclude PATTERN Exclude /regexp/ or string from run.
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
-p, --pride Pride. Show your testing pride!
Parallel Testing
Parallel testing allows you to parallelize your test suite. While forking processes is the default method, threading is supported as well. Running tests in parallel reduces the time it takes your entire test suite to run.
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 is 2, but can be changed by the number passed to the parallelize method. Active Record automatically handles creating and migrating a new database for each worker to use.
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 and migrating a 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 the tests will use the original test-database
database.
Two hooks are provided, one runs when the process is forked, and one runs before the processes are closed. These can be useful if your app uses multiple databases or perform other tasks that depend on the number of workers.
The parallelize_setup
method is called right after the processes are forked. The parallelize_teardown
metod
is called right before the processes are closed.
class ActiveSupport::TestCase
parallelize_setup do |worker|
# setup databases
end
parallelize_teardown do |worker|
# cleanup database
end
parallelize(workers: 2)
end
These methods are not needed or available when using parallel testing with threads.
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: 2, with: :threads)
end
Rails applications generated from JRuby will automatically include the with: :threads
option.
The number of workers passed to parallelize
determines the number of threads the tests will use. 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
The Test Database
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.
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.
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. 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/rails db:migrate
) will
bring the schema up to date.
NOTE: If there were modifications to existing migrations, the test database needs to
be rebuilt. This can be done by executing bin/rails db:test:prepare
.
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.
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 and written in YAML. There is one file per model.
NOTE: Fixtures are not designed to create every object that your tests need, and are best managed when only used for default data that can be applied to the common case.
You'll find fixtures under your test/fixtures
directory. When you run rails generate model
to create a new model, Rails automatically creates fixture stubs in this directory.
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!
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:
# In fixtures/categories.yml
about:
name: About
# In fixtures/articles.yml
first:
title: Welcome to Rails!
body: Hello world!
category: about
Notice the category
key of the first
article found in fixtures/articles.yml
has a value of about
. This tells Rails to load the category about
found in fixtures/categories.yml
.
NOTE: For associations to reference one another by name, you can use the fixture name instead of specifying 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.
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 %>
Fixtures in Action
Rails automatically loads all fixtures from the test/fixtures
directory by
default. 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 method in case you want to access it directly
TIP: 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).
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
users(:david)
# this will return the property for david called id
users(:david).id
# one can also access methods available on the User class
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)
Model Testing
Model tests are used to test the various models of your application.
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 title:string body:text
create test/models/article_test.rb
create test/fixtures/articles.yml
Model tests don't have their own superclass like ActionMailer::TestCase
instead they inherit from ActiveSupport::TestCase
.
System Testing
System tests allow you to test user interactions with your application, running tests in either a real or a headless browser. System tests use Capybara under the hood.
For creating Rails system tests, you use the test/system
directory in your
application. Rails provides a generator to create a system test skeleton for you.
$ 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.
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". Say you want to change the driver from Selenium to
Poltergeist. First add the poltergeist
gem to your Gemfile
. Then in your
application_system_test_case.rb
file do the following:
require "test_helper"
require "capybara/poltergeist"
class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
driven_by :poltergeist
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 your Capybara configuration requires more setup than provided by Rails, this
additional configuration could be added into the application_system_test_case.rb
file.
Please see Capybara's documentation for additional settings.
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 after_teardown
inside
Rails.
The take_screenshot
helper method can be included anywhere in your tests to
take a screenshot of the browser.
Implementing a system test
Now we're going to add a system test to our blog application. We'll demonstrate writing a system test by visiting the index page and creating 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 for us. 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 our 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
NOTE: By default, running bin/rails test
won't run your system tests.
Make sure to run bin/rails test:system
to actually run them.
Creating articles system test
Now let's test the flow for creating a new article in our blog.
test "creating an 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 create the new article in the database.
We will be redirected back to the articles index page and there we assert that the text from the new article's title is on the articles index page.
Testing for multiple screen sizes
If you want to test for mobile sizes on top of testing for desktop,
you can create another class that inherits from SystemTestCase and use 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
Taking it further
The beauty of system testing is that it is similar to integration testing in that it tests the user's interaction with your controller, model, and view, but system testing is much more robust and actually tests your application as if a real user were using it. Going forward, you can test anything that the user themselves would do in your application such as commenting, deleting articles, publishing draft articles, etc.
Integration Testing
Integration tests are used to test how various parts of your application interact. They are generally used to test important workflows within our application.
For creating Rails integration tests, we use the test/integration
directory for our application. Rails provides a generator to create an integration test skeleton for us.
$ 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
Here the test is inheriting from ActionDispatch::IntegrationTest
. This makes some additional helpers available for us to use in our integration tests.
Helpers Available for Integration Tests
In addition to the standard testing helpers, inheriting from ActionDispatch::IntegrationTest
comes with some additional helpers available when writing integration tests. Let's get briefly introduced to the three categories of helpers we get to choose from.
For dealing with the integration test runner, see ActionDispatch::Integration::Runner
.
When performing requests, we will have ActionDispatch::Integration::RequestHelpers
available for our use.
If we need to modify the session, or state of our integration test, take a look at ActionDispatch::Integration::Session
to help.
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 we 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"
end
end
We will take a look at assert_select
to query the resulting HTML of a request in the "Testing Views" section below. It is used for testing the response of our request by asserting the presence of key HTML elements and their content.
When we visit our root path, we should see welcome/index.html.erb
rendered for the view. So this assertion should pass.
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
post "/articles",
params: { article: { title: "can create", body: "article successfully." } }
assert_response :redirect
follow_redirect!
assert_response :success
assert_select "p", "Title:\n can create"
end
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.
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
follow_redirect!
The two lines following the request are to handle the redirect we setup when creating a new article.
NOTE: 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 and our new article is readable on the page.
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 editing comments. Integration tests are a great place to experiment with all kinds of use-cases for our applications.
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 are testing how your actions handle the requests and the expected result or response, in some cases an HTML view.
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?
The easiest way to see functional tests in action is to generate a controller using the scaffold generator:
$ bin/rails generate scaffold_controller article title:string body:text
...
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. Supports:json
by default.
All of these keyword arguments are optional.
Example: Calling the :show
action, passing an id
of 12 as the params
and setting HTTP_REFERER
header:
get article_url, params: { id: 12 }, headers: { "HTTP_REFERER" => "http://example.com/home" }
Another example: Calling the :update
action, passing an id
of 12 as the params
as an Ajax request.
patch article_url, params: { id: 12 }, xhr: true
NOTE: 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 articles_url, params: { article: { body: 'Rails is awesome!', title: 'Hello Rails' } }
end
assert_redirected_to article_path(Article.last)
end
Now you can try running all the tests and they should pass.
NOTE: If you followed the steps in the Basic Authentication section, you'll need to add the following to the setup
block to get all the tests passing:
request.headers['Authorization'] = ActionController::HttpAuthentication::Basic.
encode_credentials('dhh', 'secret')
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.
NOTE: 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.
Testing XHR (AJAX) requests
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.content_type
end
The Three Hashes of the Apocalypse
After a request has been made and processed, you will have 3 Hash objects ready for use:
cookies
- Any cookies that are setflash
- Any objects living in the flashsession
- 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"] flash[:gordon]
session["shmession"] session[:shmession]
cookies["are_good_for_u"] cookies[:are_good_for_u]
Instance Variables Available
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
Setting Headers and CGI variables
HTTP headers and CGI variables can be 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
Testing flash
notices
If you remember from earlier, one of the Three 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 article_url, params: { article: { title: 'Some title' } }
end
assert_redirected_to article_path(Article.last)
assert_equal 'Article was successfully created.', flash[:notice]
end
If we run our test now, we should see a failure:
$ bin/rails test test/controllers/articles_controller_test.rb -n test_should_create_article
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
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
else
render 'new'
end
end
Now if we run our tests, we should see it pass:
$ bin/rails test test/controllers/articles_controller_test.rb -n 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
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 article_url(article)
assert_response :success
end
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 article_url(article)
end
assert_redirected_to articles_path
end
We can also add 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 association to fetch updated data and assert that title is updated.
article.reload
assert_equal "updated", article.title
end
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 as what follows. Disregard the other tests for now, we're leaving them out for brevity.
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
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.
Test helpers
To avoid code duplication, you can add your own test helpers. Sign in helper can be a good example:
# 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
Testing Routes
Like everything else in your Rails application, you can test your routes. Route tests reside in test/controllers/
or are part of controller tests.
NOTE: 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
.
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. Like route tests, view tests reside in test/controllers/
or are part of controller tests. 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'
end
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
end
end
assert_select "ol" do
assert_select "li", 8
end
This assertion is quite powerful. For more advanced usage, refer to its documentation.
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.'
end
Testing Helpers
A helper is just a simple module where you can define methods which are available into 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
.
Testing Your Mailers
Testing mailer classes requires some specific tools to do a thorough job.
Keeping the Postman in Check
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
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.
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.
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.
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.
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
# 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 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.
NOTE: email.body.to_s
is present when there's only one (HTML or text) part present.
If the mailer provides both, you can test your fixture against specific parts
with email.text_part.body.to_s
or email.html_part.body.to_s
.
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
).
NOTE: The ActionMailer::Base.deliveries
array is only reset automatically in
ActionMailer::TestCase
and ActionDispatch::IntegrationTest
tests.
If you want to have a clean slate outside these test cases, you can reset it
manually with: ActionMailer::Base.deliveries.clear
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 UsersControllerTest < ActionDispatch::IntegrationTest
test "invite friend" do
assert_difference 'ActionMailer::Base.deliveries.size', +1 do
post invite_friend_url, params: { 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.to_s)
end
end
Testing Jobs
Since your custom jobs can be queued at different levels inside your application, you'll need to test both the jobs themselves (their behavior when they get enqueued) and that other entities correctly enqueue them.
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)
end
end
This test is pretty simple and only asserts that the job got 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.
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
product.charge(account)
end
end
end
Additional Testing Resources
Testing Time-Dependent Code
Rails provides built-in helper methods that enable you to assert that your time-sensitive code works as expected.
Here is an example using the travel_to
helper:
# Lets say that 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
assert_equal Date.new(2004, 10, 24), user.activation_date # inside the `travel_to` block `Date.current` is mocked
assert user.applicable_for_gifting?
end
assert_equal Date.new(2004, 10, 24), user.activation_date # The change was visible only inside the `travel_to` block.
Please see ActiveSupport::Testing::TimeHelpers
API Documentation
for in-depth information about the available time helpers.