System tests were added to the Rails stack in Rails 5.1. When I sat down to start using them, I found it hard to gather relevant, up to date information that is not about RSpec. Here’s all the latest and greatest that I collected on working with the system tests with Minitest.
Introduction to System Tests
The configuration is so simple, it's almost confusing.
The Capybara gem is used for interacting with the browser. It's through Capybara that we can make the tests visit pages, fill in forms, click on links and buttons. If you've worked with Capybara before, you're aware of all the things you have to coordinate to make it work with a database cleaning strategy and the browser configuration. Hooray for the Rails system test set up: it takes care of all the configuration that is needed to work with Capybara out-of-the-box. So we can focus on the actual test writing. It uses the Selenium driver by default.
All the settings are available through
application_system_test_case.rb. The only thing you need to do is require this in each test file.
1#application_system_test_case.rb (default) 2 3 4require "test_helper" 5 6class ApplicationSystemTestCase < ActionDispatch::SystemTestCase 7 driven_by :selenium, using: :chrome, screen_size: [1400, 1400] 8end
If you generated a new app with Rails 6, this is really all you need. Meaning: you can skip all the advice on how to set up the Selenium driver that the Internet shows for user interface tests or RSpec's feature tests.
In existing apps, generating a scaffold will automatically generate the
application_system_test_case.rb and everything you need for the system tests.
When Eileen Uchitelle introduced system tests, Chrome was chosen over Firefox because at the time FF didn't play nicely with Selenium. That is fixed in later versions of Firefox. So I replace Chrome with FF, like so:
1#application_system_test_case.rb (change driver to Firefox) 2 3require "test_helper" 4 5class ApplicationSystemTestCase < ActionDispatch::SystemTestCase 6 driven_by :selenium, using: :firefox, screen_size: [1400, 1400] 7end
(Initially, I ran
$ rails db:test:prepare after switching drivers to ensure a clean start, BUT the new test runner takes care of that too: invoking test will autorun
New in Rails 6
Since the introduction of system tests in 5.1, the chromedriver-helper gem has been deprecated. In new Rails 6 apps, it is replaced with the webdrivers gem. In Rails 5 apps, you should replace the chromedriver-helper with the webdrivers gem if you haven't done that yet. With the webdrivers gem in place, you don't even need the selenium-webdriver gem; webdrivers takes care of that one too. Fun fact: Rails 6 gives us both the selenium-webdriver gem and the webdrivers gem.
Sanity Check: What You Don't Need Anymore
Setting up Capybara used to be a pain. It wasn't clear what you needed to set it up from scratch, including finding the correct database cleaning strategy, the dependencies of the capybara-webkit gem and all kinds of unexpected requirements that you needed to figure out before you could start writing tests. Now that Rails provides everything we need, I found the only confusing part to be all the information available in guides and documentation that is obsolete now. Here are some things that we can ignore now.
First, the precooked Rails setup means that we can omit more gems that are often mentioned in regards to testing, like minitest-rails-capybara, or the extras for Minitest: like-colored output, fast failing tests and running one line/test. These Minitest features are in the test runner introduced in Rails 5.0.
There's no need for the database_cleaner gem anymore; Rails does the cleanup for us ('transactional tests').
You don't even need to use Capybara's
save_and_open_screenshot, because Rails provides a
take_screenshot method. It saves a screenshot in
/tmp and provides a link in the test output for easy access.
Choosing Between a Real Browser and Headless Browser
I can't get enough of watching the system tests running in the browser and see how all the links are clicked, forms are filled in, etc. But, it is slow. To speed up the test run, you can use a 'headless' browser: that is a browser that has the same access to your app as a regular browser, but without the graphical user interface. Meaning: it works the same but you don't actually see the tests doing their work since a headless driver doesn't open an actual browser window.
If you do want to go headless, there's
headless_firefox. To use them, there's one small change needed:
1# To change driver to headless_* 2#application_system_test_case.rb (change driver to headless_*:) 3 4require "test_helper" 5 6class ApplicationSystemTestCase < ActionDispatch::SystemTestCase 7 driven_by :selenium, using: :headless_firefox 8end
Note: In the Rails documentation and in several articles I found, Poltergeist was named as an option for the driver. It used to be popular as the - headless - PhantomJS driver for Capybara. PhantomJS has been abandoned. So, no need to dive into the particulars—the reason I mention it here is because Poltergeist and PhantomJS are still mentioned in the Rails docs.
There's more customization you can do, but to get started, this is really all you need.
Running the Tests
$ rails test will run all the tests except the system tests. You need to explicitly run
$ rails test:system. (Fun fact: the
$ rails command will always run through bin/rails. No need to type
$ bin/rails anymore.)
- Run all the system tests:
$ rails test:system
- Run test in a specific file (here: users_test.rb)
$ rails test/system/users_test
- ... or one specific test:
$ rails test test/system/users_test.rb:21
- To run all the tests: run the system tests first:
$ rails test:system test
Note: the options flags don't work with
test:system; if you want to use flags like
-f (for fail fast) or
-v (for verbose), use
$ rails test test/system -v -f
What (Not) to Test
System tests are complementary to unit tests, not a substitute. It will do to test a happy path, plus maybe one path with an error message or redirect. System tests are not meant to test all the edge cases in the browser; just cover the main features.
When choosing my test subject, I try to find an entity to test that reflects how the user uses the app. For the naming of my tests, I borrowed GitLab's naming convention of ROLE_ACTION_test.rb, which fits this approach well. For instance:
General Tips and Tricks
- If you use Devise for authentication, you can use the Devise integration helpers to log in and log out test users. Add
include Devise::Test::IntegrationHelpersto a test class, or add it in the
test_helper.rbfile to make them available in all tests. Now you can create a user and
sign_in(@user). If you put that in a
setupmethod, you don’t need to log out the user in a teardown. Rails takes care of cleaning up what's in the setup method.
- Working with forms, it's tempting to reference the ids that Rails creates automatically from model name + field name and the button types for
click_on :commit). But since systems tests are about what a user would actually see on their screen, it makes sense to use visible elements, i.e. texts. A reasonable option would be to have reference keys in i18n locale files and use those keys instead of the ever-changing literal texts. (
fill_in :user_email). Capybara finds the text only with the full I18n syntax:
assert_selector "h1", text: I18n.t("activerecord.models.things").
- The path helpers are included by default. For some libraries you need to include the helpers in the test class, for instance
include ActionMailer::TestHelper, to use the
- Create custom classes to run the tests on different screen sizes. Check out the guides.
- The screenshot feature can also be used to take screenshots for your documentation and promotional materials. If you make it a screencast and slow down the playback speed, you have a product video in minutes!
- Rails provides a generator for system tests.
- Minitest in Rails is slightly different than Minitest itself, and also adds Rails specific methods and assertions. Check the Rails docs first before the Minitest docs.
I had good fun with the system tests, and that was, for the most part, thanks to how easy it was to use it out-of-the-box.
In this post, we looked at what configuration Rails delivers out-of-the-box and what minimal customizations we may want to add. Minitest is great for writing System tests. A few tips and tricks should help to get your first system tests up and running. Watch them do their magic in the browser!