Testing best practices

Test speed

GitLab has a massive test suite that, without parallelization, can take hours to run. It's important that we make an effort to write tests that are accurate and effective as well as fast.

Here are some things to keep in mind regarding test performance:

  • double and spy are faster than FactoryBot.build(...)
  • FactoryBot.build(...) and .build_stubbed are faster than .create.
  • Don't create an object when build, build_stubbed, attributes_for, spy, or double will do. Database persistence is slow!
  • Don't mark a feature as requiring JavaScript (through :js in RSpec) unless it's actually required for the test to be valid. Headless browser testing is slow!

RSpec

General guidelines

  • Use a single, top-level describe ClassName block.
  • Use .method to describe class methods and #method to describe instance methods.
  • Use context to test branching logic.
  • Try to match the ordering of tests to the ordering within the class.
  • Try to follow the Four-Phase Test pattern, using newlines to separate phases.
  • Use Gitlab.config.gitlab.host rather than hard coding 'localhost'
  • Don't assert against the absolute value of a sequence-generated attribute (see Gotchas).
  • Don't supply the :each argument to hooks since it's the default.
  • On before and after hooks, prefer it scoped to :context over :all
  • When using evaluate_script("$('.js-foo').testSomething()") (or execute_script) which acts on a given element, use a Capyabara matcher beforehand (e.g. find('.js-foo')) to ensure the element actually exists.

System / Feature tests

Note: Before writing a new system test, please consider not writing one!
  • Feature specs should be named ROLE_ACTION_spec.rb, such as user_changes_password_spec.rb.
  • Use scenario titles that describe the success and failure paths.
  • Avoid scenario titles that add no information, such as "successfully".
  • Avoid scenario titles that repeat the feature title.
  • Create only the necessary records in the database
  • Test a happy path and a less happy path but that's it
  • Every other possible path should be tested with Unit or Integration tests
  • Test what's displayed on the page, not the internals of ActiveRecord models. For instance, if you want to verify that a record was created, add expectations that its attributes are displayed on the page, not that Model.count increased by one.
  • It's ok to look for DOM elements but don't abuse it since it makes the tests more brittle

Debugging Capybara

Sometimes you may need to debug Capybara tests by observing browser behavior.

Live debug

You can pause Capybara and view the website on the browser by using the live_debug method in your spec. The current page will be automatically opened in your default browser. You may need to sign in first (the current user's credentials are displayed in the terminal).

To resume the test run, press any key.

For example:

$ bin/rspec spec/features/auto_deploy_spec.rb:34
Running via Spring preloader in process 8999
Run options: include {:locations=>{"./spec/features/auto_deploy_spec.rb"=>[34]}}

Current example is paused for live debugging
The current user credentials are: user2 / 12345678
Press any key to resume the execution of the example!
Back to the example!
.

Finished in 34.51 seconds (files took 0.76702 seconds to load)
1 example, 0 failures

Note: live_debug only works on javascript enabled specs.

Run :js spec in a visible browser

Run the spec with CHROME_HEADLESS=0, e.g.:

CHROME_HEADLESS=0 bundle exec rspec some_spec.rb

The test will go by quickly, but this will give you an idea of what's happening.

You can also add byebug or binding.pry to pause execution and step through the test.

Screenshots

We use the capybara-screenshot gem to automatically take a screenshot on failure. In CI you can download these files as job artifacts.

Also, you can manually take screenshots at any point in a test by adding the methods below. Be sure to remove them when they are no longer needed! See https://github.com/mattheworiordan/capybara-screenshot#manual-screenshots for more.

Add screenshot_and_save_page in a :js spec to screenshot what Capybara "sees", and save the page source.

Add screenshot_and_open_image in a :js spec to screenshot what Capybara "sees", and automatically open the image.

Fast unit tests

Some classes are well-isolated from Rails and you should be able to test them without the overhead added by the Rails environment and Bundler's :default group's gem loading. In these cases, you can require 'fast_spec_helper' instead of require 'spec_helper' in your test file, and your test should run really fast since:

  • Gems loading is skipped
  • Rails app boot is skipped
  • gitlab-shell and Gitaly setup are skipped
  • Test repositories setup are skipped

fast_spec_helper also support autoloading classes that are located inside the lib/ directory. It means that as long as your class / module is using only code from the lib/ directory you will not need to explicitly load any dependencies. fast_spec_helper also loads all ActiveSupport extensions, including core extensions that are commonly used in the Rails environment.

Note that in some cases, you might still have to load some dependencies using require_dependency when a code is using gems or a dependency is not located in lib/.

For example, if you want to test your code that is calling the Gitlab::UntrustedRegexp class, which under the hood uses re2 library, you should either add require_dependency 're2' to files in your library that need re2 gem, to make this requirement explicit, or you can add it to the spec itself, but the former is preferred.

It takes around one second to load tests that are using fast_spec_helper instead of 30+ seconds in case of a regular spec_helper.

let variables

GitLab's RSpec suite has made extensive use of let variables to reduce duplication. However, this sometimes comes at the cost of clarity, so we need to set some guidelines for their use going forward:

  • let variables are preferable to instance variables. Local variables are preferable to let variables.
  • Use let to reduce duplication throughout an entire spec file.
  • Don't use let to define variables used by a single test; define them as local variables inside the test's it block.
  • Don't define a let variable inside the top-level describe block that's only used in a more deeply-nested context or describe block. Keep the definition as close as possible to where it's used.
  • Try to avoid overriding the definition of one let variable with another.
  • Don't define a let variable that's only used by the definition of another. Use a helper method instead.

set variables

In some cases there is no need to recreate the same object for tests again for each example. For example, a project is needed to test issues on the same project, one project will do for the entire file. This can be achieved by using set in the same way you would use let.

rspec-set only works on ActiveRecord objects, and before new examples it reloads or recreates the model, only if needed. That is, when you changed properties or destroyed the object.

There is one gotcha; you can't reference a model defined in a let block in a set block.

Time-sensitive tests

Timecop is available in our Ruby-based tests for verifying things that are time-sensitive. Any test that exercises or verifies something time-sensitive should make use of Timecop to prevent transient test failures.

Example:

it 'is overdue' do
  issue = build(:issue, due_date: Date.tomorrow)

  Timecop.freeze(3.days.from_now) do
    expect(issue).to be_overdue
  end
end

Table-based / Parameterized tests

This style of testing is used to exercise one piece of code with a comprehensive range of inputs. By specifying the test case once, alongside a table of inputs and the expected output for each, your tests can be made easier to read and more compact.

We use the rspec-parameterized gem. A short example, using the table syntax and checking Ruby equality for a range of inputs, might look like this:

describe "#==" do
  using RSpec::Parameterized::TableSyntax

  let(:project1) { create(:project) }
  let(:project2) { create(:project) }
  where(:a, :b, :result) do
    1         | 1        | true
    1         | 2        | false
    true      | true     | true
    true      | false    | false
    project1  | project1 | true
    project2  | project2 | true
    project 1 | project2 | false
  end

  with_them do
    it { expect(a == b).to eq(result) }

    it 'is isomorphic' do
      expect(b == a).to eq(result)
    end
  end
end

Prometheus tests

Prometheus metrics may be preserved from one test run to another. To ensure that metrics are reset before each example, add the :prometheus tag to the Rspec test.

Matchers

Custom matchers should be created to clarify the intent and/or hide the complexity of RSpec expectations.They should be placed under spec/support/matchers/. Matchers can be placed in subfolder if they apply to a certain type of specs only (e.g. features, requests etc.) but shouldn't be if they apply to multiple type of specs.

have_gitlab_http_status

Prefer have_gitlab_http_status over have_http_status because the former could also show the response body whenever the status mismatched. This would be very useful whenever some tests start breaking and we would love to know why without editing the source and rerun the tests.

This is especially useful whenever it's showing 500 internal server error.

Shared contexts

All shared contexts should be be placed under spec/support/shared_contexts/. Shared contexts can be placed in subfolder if they apply to a certain type of specs only (e.g. features, requests etc.) but shouldn't be if they apply to multiple type of specs.

Each file should include only one context and have a descriptive name, e.g. spec/support/shared_contexts/controllers/githubish_import_controller_shared_context.rb.

Shared examples

All shared examples should be be placed under spec/support/shared_examples/. Shared examples can be placed in subfolder if they apply to a certain type of specs only (e.g. features, requests etc.) but shouldn't be if they apply to multiple type of specs.

Each file should include only one context and have a descriptive name, e.g. spec/support/shared_examples/controllers/githubish_import_controller_shared_example.rb.

Helpers

Helpers are usually modules that provide some methods to hide the complexity of specific RSpec examples. You can define helpers in RSpec files if they're not intended to be shared with other specs. Otherwise, they should be be placed under spec/support/helpers/. Helpers can be placed in subfolder if they apply to a certain type of specs only (e.g. features, requests etc.) but shouldn't be if they apply to multiple type of specs.

Helpers should follow the Rails naming / namespacing convention. For instance spec/support/helpers/cycle_analytics_helpers.rb should define:

module Spec
  module Support
    module Helpers
      module CycleAnalyticsHelpers
        def create_commit_referencing_issue(issue, branch_name: random_git_name)
          project.repository.add_branch(user, branch_name, 'master')
          create_commit("Commit for ##{issue.iid}", issue.project, user, branch_name)
        end
      end
    end
  end
end

Helpers should not change the RSpec config. For instance, the helpers module described above should not include:

RSpec.configure do |config|
  config.include Spec::Support::Helpers::CycleAnalyticsHelpers
end

Factories

GitLab uses factory_bot as a test fixture replacement.

  • Factory definitions live in spec/factories/, named using the pluralization of their corresponding model (User factories are defined in users.rb).
  • There should be only one top-level factory definition per file.
  • FactoryBot methods are mixed in to all RSpec groups. This means you can (and should) call create(...) instead of FactoryBot.create(...).
  • Make use of traits to clean up definitions and usages.
  • When defining a factory, don't define attributes that are not required for the resulting record to pass validation.
  • When instantiating from a factory, don't supply attributes that aren't required by the test.
  • Factories don't have to be limited to ActiveRecord objects. See example.

Fixtures

All fixtures should be be placed under spec/fixtures/.

Config

RSpec config files are files that change the RSpec config (i.e. RSpec.configure do |config| blocks). They should be placed under spec/support/.

Each file should be related to a specific domain, e.g. spec/support/capybara.rb, spec/support/carrierwave.rb, etc.

If a helpers module applies only to a certain kind of specs, it should add modifiers to the config.include call. For instance if spec/support/helpers/cycle_analytics_helpers.rb applies to :lib and type: :model specs only, you would write the following:

RSpec.configure do |config|
  config.include Spec::Support::Helpers::CycleAnalyticsHelpers, :lib
  config.include Spec::Support::Helpers::CycleAnalyticsHelpers, type: :model
end

If a config file only consists of config.include, you can add these config.include directly in spec/spec_helper.rb.

For very generic helpers, consider including them in the spec/support/rspec.rb file which is used by the spec/fast_spec_helper.rb file. See Fast unit tests for more details about the spec/fast_spec_helper.rb file.


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