Testing best practices

Test Design

Testing at GitLab is a first class citizen, not an afterthought. It's important we consider the design of our tests as we do the design of our features.

When implementing a feature, we think about developing the right capabilities the right way. This helps us narrow our scope to a manageable level. When implementing tests for a feature, we must think about developing the right tests, but then cover all the important ways the test may fail. This can quickly widen our scope to a level that is difficult to manage.

Test heuristics can help solve this problem. They concisely address many of the common ways bugs manifest themselves in our code. When designing our tests, take time to review known test heuristics to inform our test design. We can find some helpful heuristics documented in the Handbook in the Test Engineering section.

RSpec

To run RSpec tests:

# run test for a file
bin/rspec spec/models/project_spec.rb

# run test for the example on line 10 on that file
bin/rspec spec/models/project_spec.rb:10

# run tests matching the example name has that string
bin/rspec spec/models/project_spec.rb -e associations

# run all tests, will take hours for GitLab codebase!
bin/rspec

Use Guard to continuously monitor for changes and only run matching tests:

bundle exec guard

When using spring and guard together, use SPRING=1 bundle exec guard instead to make use of spring.

Ruby warnings

Introduced in GitLab 13.7.

We've enabled deprecation warnings by default when running specs. Making these warnings more visible to developers helps upgrading to newer Ruby versions.

You can silence deprecation warnings by setting the environment variable SILENCE_DEPRECATIONS, for example:

# silence all deprecation warnings
SILENCE_DEPRECATIONS=1 bin/rspec spec/models/project_spec.rb

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.

Test performance is important to maintaining quality and velocity, and has a direct impact on CI build times and thus fixed costs. We want thorough, correct, and fast tests. Here you can find some information about tools and techniques available to you to achieve that.

Don't request capabilities you don't need

We make it easy to add capabilities to our examples by annotating the example or a parent context. Examples of these are:

:js in feature specs, which runs a full JavaScript capable headless browser.
:clean_gitlab_redis_cache which provides a clean Redis cache to the examples.
:request_store which provides a request store to the examples.

We should reduce test dependencies, and avoiding capabilities also reduces the amount of set-up needed.

:js is particularly important to avoid. This must only be used if the feature test requires JavaScript reactivity in the browser. Using a headless browser is much slower than parsing the HTML response from the app.

Optimize factory usage

A common cause of slow tests is excessive creation of objects, and thus computation and DB time. Factories are essential to development, but they can make inserting data into the DB so easy that we may be able to optimize.

The two basic techniques to bear in mind here are:

Reduce: avoid creating objects, and avoid persisting them.
Reuse: shared objects, especially nested ones we do not examine, can generally be shared.

To avoid creation, it is worth bearing in mind that:

instance_double and spy are faster than FactoryBot.build(...).
FactoryBot.build(...) and .build_stubbed are faster than .create.
Don't create an object when you can use build, build_stubbed, attributes_for, spy, or instance_double. Database persistence is slow!

Use Factory Doctor to find cases where database persistence is not needed in a given test.

# run test for path
FDOC=1 bin/rspec spec/[path]/[to]/[spec].rb

A common change is to use build or build_stubbed instead of create:

# Old
let(:project) { create(:project) }

# New
let(:project) { build(:project) }

Factory Profiler can help to identify repetitive database persistence via factories.

# run test for path
FPROF=1 bin/rspec spec/[path]/[to]/[spec].rb

# to visualize with a flamegraph
FPROF=flamegraph bin/rspec spec/[path]/[to]/[spec].rb

A common change is to use let_it_be:

# Old
let(:project) { create(:project) }

# New
let_it_be(:project) { create(:project) }

A common cause of a large number of created factories is factory cascades, which result when factories create and recreate associations. They can be identified by a noticeable difference between total time and top-level time numbers:

   total   top-level     total time      time per call      top-level time               name

     208           0        9.5812s            0.0461s             0.0000s          namespace
     208          76       37.4214s            0.1799s            13.8749s            project

The table above shows us that we never create any namespace objects explicitly (top-level == 0) - they are all created implicitly for us. But we still end up with 208 of them (one for each project) and this takes 9.5 seconds.

In order to reuse a single object for all calls to a named factory in implicit parent associations, FactoryDefault can be used:

RSpec.describe API::Search, factory_default: :keep do
  let_it_be(:namespace) { create_default(:namespace) }

Then every project we create uses this namespace, without us having to pass it as namespace: namespace. In order to make it work along with let_it_be, factory_default: :keep must be explicitly specified. That keeps the default factory for every example in a suite instead of recreating it for each example.

To prevent accidental reliance between test examples, objects created with create_default are frozen.

Maybe we don't need to create 208 different projects - we can create one and reuse it. In addition, we can see that only about 1/3 of the projects we create are ones we ask for (76/208). There is benefit in setting a default value for projects as well:

  let_it_be(:project) { create_default(:project) }

In this case, the total time and top-level time numbers match more closely:

   total   top-level     total time      time per call      top-level time               name

      31          30        4.6378s            0.1496s             4.5366s            project
       8           8        0.0477s            0.0477s             0.0477s          namespace

Identify slow tests

Running a spec with profiling is a good way to start optimizing a spec. This can be done with:

bundle exec rspec --profile -- path/to/spec_file.rb

Which includes information like the following:

Top 10 slowest examples (10.69 seconds, 7.7% of total time):
  Issue behaves like an editable mentionable creates new cross-reference notes when the mentionable text is edited
    1.62 seconds ./spec/support/shared_examples/models/mentionable_shared_examples.rb:164
  Issue relative positioning behaves like a class that supports relative positioning .move_nulls_to_end manages to move nulls to the end, stacking if we cannot create enough space
    1.39 seconds ./spec/support/shared_examples/models/relative_positioning_shared_examples.rb:88
  Issue relative positioning behaves like a class that supports relative positioning .move_nulls_to_start manages to move nulls to the end, stacking if we cannot create enough space
    1.27 seconds ./spec/support/shared_examples/models/relative_positioning_shared_examples.rb:180
  Issue behaves like an editable mentionable behaves like a mentionable extracts references from its reference property
    0.99253 seconds ./spec/support/shared_examples/models/mentionable_shared_examples.rb:69
  Issue behaves like an editable mentionable behaves like a mentionable creates cross-reference notes
    0.94987 seconds ./spec/support/shared_examples/models/mentionable_shared_examples.rb:101
  Issue behaves like an editable mentionable behaves like a mentionable when there are cached markdown fields sends in cached markdown fields when appropriate
    0.94148 seconds ./spec/support/shared_examples/models/mentionable_shared_examples.rb:86
  Issue behaves like an editable mentionable when there are cached markdown fields when the markdown cache is stale persists the refreshed cache so that it does not have to be refreshed every time
    0.92833 seconds ./spec/support/shared_examples/models/mentionable_shared_examples.rb:153
  Issue behaves like an editable mentionable when there are cached markdown fields refreshes markdown cache if necessary
    0.88153 seconds ./spec/support/shared_examples/models/mentionable_shared_examples.rb:130
  Issue behaves like an editable mentionable behaves like a mentionable generates a descriptive back-reference
    0.86914 seconds ./spec/support/shared_examples/models/mentionable_shared_examples.rb:65
  Issue#related_issues returns only authorized related issues for given user
    0.84242 seconds ./spec/models/issue_spec.rb:335

Finished in 2 minutes 19 seconds (files took 1 minute 4.42 seconds to load)
277 examples, 0 failures, 1 pending

From this result, we can see the most expensive examples in our spec, giving us a place to start. The most expensive examples here are in shared examples; any reductions generally have a larger impact as they are called in multiple places.

Avoid repeating expensive actions

While isolated examples are very clear, and help serve the purpose of specs as specification, the following example shows how we can combine expensive actions:

subject { described_class.new(arg_0, arg_1) }

it 'creates an event' do
  expect { subject.execute }.to change(Event, :count).by(1)
end

it 'sets the frobulance' do
  expect { subject.execute }.to change { arg_0.reset.frobulance }.to('wibble')
end

it 'schedules a background job' do
  expect(BackgroundJob).to receive(:perform_async)

  subject.execute
end

If the call to subject.execute is expensive, then we are repeating the same action just to make different assertions. We can reduce this repetition by combining the examples:

it 'performs the expected side-effects' do
  expect(BackgroundJob).to receive(:perform_async)

  expect { subject.execute }
    .to change(Event, :count).by(1)
    .and change { arg_0.frobulance }.to('wibble')
end

Be careful doing this, as this sacrifices clarity and test independence for performance gains.

When combining tests, consider using :aggregate_failures, so that the full results are available, and not just the first failure.

General guidelines

Use a single, top-level RSpec.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 in 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).
Avoid using expect_any_instance_of or allow_any_instance_of (see Gotchas).
Don't supply the :each argument to hooks because 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 Capybara matcher beforehand (such as find('.js-foo')) to ensure the element actually exists.
Use focus: true to isolate parts of the specs you want to run.
Use :aggregate_failures when there is more than one expectation in a test.
For empty test description blocks, use specify rather than it do if the test is self-explanatory.
Use non_existing_record_id/non_existing_record_iid/non_existing_record_access_level when you need an ID/IID/access level that doesn't actually exists. Using 123, 1234, or even 999 is brittle as these IDs could actually exist in the database in the context of a CI run.

Coverage

simplecov is used to generate code test coverage reports. These are generated automatically on the CI, but not when running tests locally. To generate partial reports when you run a spec file on your machine, set the SIMPLECOV environment variable:

SIMPLECOV=1 bundle exec rspec spec/models/repository_spec.rb

Coverage reports are generated into the coverage folder in the app root, and you can open these in your browser, for example:

firefox coverage/index.html

Use the coverage reports to ensure your tests cover 100% of your code.

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, because it makes the tests more brittle

UI testing

When testing the UI, write tests that simulate what a user sees and how they interact with the UI. This means preferring Capybara's semantic methods and avoiding querying by IDs, classes, or attributes.

The benefits of testing in this way are that:

It ensures all interactive elements have an accessible name.
It is more readable, as it uses more natural language.
It is less brittle, as it avoids querying by IDs, classes, and attributes, which are not visible to the user.

We strongly recommend that you query by the element's text label instead of by ID, class name, or data-testid.

If needed, you can scope interactions within a specific area of the page by using within. As you will likely be scoping to an element such as a div, which typically does not have a label, you may use a data-testid selector in this case.

Actions

Where possible, use more specific actions, such as the ones below.

# good
click_button 'Submit review'

click_link 'UI testing docs'

fill_in 'Search projects', with: 'gitlab' # fill in text input with text

select 'Last updated', from: 'Sort by' # select an option from a select input

check 'Checkbox label'
uncheck 'Checkbox label'

choose 'Radio input label'

attach_file('Attach a file', '/path/to/file.png')

# bad - interactive elements must have accessible names, so
# we should be able to use one of the specific actions above
find('.group-name', text: group.name).click
find('.js-show-diff-settings').click
find('[data-testid="submit-review"]').click
find('input[type="checkbox"]').click
find('.search').native.send_keys('gitlab')

Finders

Where possible, use more specific finders, such as the ones below.

# good
find_button 'Submit review'
find_button 'Submit review', disabled: true

find_link 'UI testing docs'
find_link 'UI testing docs', href: docs_url

find_field 'Search projects'
find_field 'Search projects', with: 'gitlab' # find the input field with text
find_field 'Search projects', disabled: true
find_field 'Checkbox label', checked: true
find_field 'Checkbox label', unchecked: true

# acceptable when finding a element that is not a button, link, or field
find('[data-testid="element"]')

Matchers

Where possible, use more specific matchers, such as the ones below.

# good
expect(page).to have_button 'Submit review'
expect(page).to have_button 'Submit review', disabled: true
expect(page).to have_button 'Notifications', class: 'is-checked' # assert the "Notifications" GlToggle is checked

expect(page).to have_link 'UI testing docs'
expect(page).to have_link 'UI testing docs', href: docs_url # assert the link has an href

expect(page).to have_field 'Search projects'
expect(page).to have_field 'Search projects', disabled: true
expect(page).to have_field 'Search projects', with: 'gitlab' # assert the input field has text

expect(page).to have_checked_field 'Checkbox label'
expect(page).to have_unchecked_field 'Radio input label'

expect(page).to have_select 'Sort by'
expect(page).to have_select 'Sort by', selected: 'Last updated' # assert the option is selected
expect(page).to have_select 'Sort by', options: ['Last updated', 'Created date', 'Due date'] # assert an exact list of options
expect(page).to have_select 'Sort by', with_options: ['Created date', 'Due date'] # assert a partial list of options

expect(page).to have_text 'Some paragraph text.'
expect(page).to have_text 'Some paragraph text.', exact: true # assert exact match

expect(page).to have_current_path 'gitlab/gitlab-test/-/issues'

expect(page).to have_title 'Not Found'

# acceptable when a more specific matcher above is not possible
expect(page).to have_css 'h2', text: 'Issue title'
expect(page).to have_css 'p', text: 'Issue description', exact: true
expect(page).to have_css '[data-testid="weight"]', text: 2
expect(page).to have_css '.atwho-view ul', visible: true

Other useful methods

After you retrieve an element using a finder method, you can invoke a number of element methods on it, such as hover.

Capybara tests also have a number of session methods available, such as accept_confirm.

Some other useful methods are shown below:

refresh # refresh the page

send_keys([:shift, 'i']) # press Shift+I keys to go to the Issues dashboard page

current_window.resize_to(1000, 1000) # resize the window

scroll_to(find_field('Comment')) # scroll to an element

You can also find a number of GitLab custom helpers in the spec/support/helpers/ directory.

Live debug

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

You can pause Capybara and view the website on the browser by using the live_debug method in your spec. The current page is 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

live_debug only works on JavaScript enabled specs.

Run `:js` spec in a visible browser

Run the spec with CHROME_HEADLESS=0, like this:

CHROME_HEADLESS=0 bin/rspec some_spec.rb

The test completes quickly, but this gives you an idea of what's happening. Using live_debug with CHROME_HEADLESS=0 pauses the open browser, and does not open the page again. This can be used to debug and inspect elements.

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.

The HTML dumps created by this are missing CSS. This results in them looking very different from the actual application. There is a small hack to add CSS which makes debugging easier.

Fast unit tests

Some classes are well-isolated from Rails. 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 because:

Gem 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. If your class or module is using only code from the lib/ directory, you don't 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. This approach is preferred.
Add it to the spec itself.

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.

`subject` and `let` variables

The GitLab RSpec suite has made extensive use of let(along with its strict, non-lazy version 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. let variables are preferable to let! 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.
let! variables should be used only in case if strict evaluation with defined order is required, otherwise let suffices. Remember that let is lazy and won't be evaluated until it is referenced.
Avoid referencing subject in examples. Use a named subject subject(:name), or a let variable instead, so the variable has a contextual name.
If the subject is never referenced inside examples, then it's acceptable to define the subject without a name.

Common test setup

In some cases, there is no need to recreate the same object for tests again for each example. For example, a project and a guest of that project are needed to test issues on the same project, so one project and user are enough for the entire file.

As much as possible, do not implement this using before(:all) or before(:context). If you do, you would need to manually clean up the data as those hooks run outside a database transaction.

Instead, this can be achieved by using let_it_be variables and the before_all hook from the test-prof gem.

let_it_be(:project) { create(:project) }
let_it_be(:user) { create(:user) }

before_all do
  project.add_guest(user)
end

This results in only one Project, User, and ProjectMember created for this context.

let_it_be and before_all are also available in nested contexts. Cleanup after the context is handled automatically using a transaction rollback.

Note that if you modify an object defined inside a let_it_be block, then you must do one of the following:

Reload the object as needed.
Use the let_it_be_with_reload alias.
Specify the reload option to reload for every example.

let_it_be_with_reload(:project) { create(:project) }
let_it_be(:project, reload: true) { create(:project) }

You can also use the let_it_be_with_refind alias, or specify the refind option as well to completely load a new object.

let_it_be_with_refind(:project) { create(:project) }
let_it_be(:project, refind: true) { create(:project) }

Time-sensitive tests

ActiveSupport::Testing::TimeHelpers can be used to verify things that are time-sensitive. Any test that exercises or verifies something time-sensitive should make use of these helpers to prevent transient test failures.

Example:

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

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

Feature flags in tests

This section was moved to developing with feature flags.

Pristine test environments

The code exercised by a single GitLab test may access and modify many items of data. Without careful preparation before a test runs, and cleanup afterward, a test can change data in a way that affects the behavior of following tests. This should be avoided at all costs! Fortunately, the existing test framework handles most cases already.

When the test environment does get polluted, a common outcome is flaky tests. Pollution often manifests as an order dependency: running spec A followed by spec B reliably fails, but running spec B followed by spec A reliably succeeds. In these cases, you can use rspec --bisect (or a manual pairwise bisect of spec files) to determine which spec is at fault. Fixing the problem requires some understanding of how the test suite ensures the environment is pristine. Read on to discover more about each data store!

SQL database

This is managed for us by the database_cleaner gem. Each spec is surrounded in a transaction, which is rolled back after the test completes. Certain specs instead issue DELETE FROM queries against every table after completion. This allows the created rows to be viewed from multiple database connections, which is important for specs that run in a browser, or migration specs, among others.

One consequence of using these strategies, instead of the well-known TRUNCATE TABLES approach, is that primary keys and other sequences are not reset across specs. So if you create a project in spec A, then create a project in spec B, the first has id=1, while the second has id=2.

This means that specs should never rely on the value of an ID, or any other sequence-generated column. To avoid accidental conflicts, specs should also avoid manually specifying any values in these kinds of columns. Instead, leave them unspecified, and look up the value after the row is created.

Redis

GitLab stores two main categories of data in Redis: cached items, and Sidekiq jobs.

In most specs, the Rails cache is actually an in-memory store. This is replaced between specs, so calls to Rails.cache.read and Rails.cache.write are safe. However, if a spec makes direct Redis calls, it should mark itself with the :clean_gitlab_redis_cache, :clean_gitlab_redis_shared_state or :clean_gitlab_redis_queues traits as appropriate.

Background jobs / Sidekiq

By default, Sidekiq jobs are enqueued into a jobs array and aren't processed. If a test queues Sidekiq jobs and need them to be processed, the :sidekiq_inline trait can be used.

The :sidekiq_might_not_need_inline trait was added when Sidekiq inline mode was changed to fake mode to all the tests that needed Sidekiq to actually process jobs. Tests with this trait should be either fixed to not rely on Sidekiq processing jobs, or their :sidekiq_might_not_need_inline trait should be updated to :sidekiq_inline if the processing of background jobs is needed/expected.

The usage of perform_enqueued_jobs is useful only for testing delayed mail deliveries, because our Sidekiq workers aren't inheriting from ApplicationJob / ActiveJob::Base.

DNS

DNS requests are stubbed universally in the test suite (as of !22368), as DNS can cause issues depending on the developer's local network. There are RSpec labels available in spec/support/dns.rb which you can apply to tests if you need to bypass the DNS stubbing, like this:

it "really connects to Prometheus", :permit_dns do

And if you need more specific control, the DNS blocking is implemented in spec/support/helpers/dns_helpers.rb and these methods can be called elsewhere.

Stubbing File methods

In the situations where you need to stub methods such as File.read, make sure to:

Stub File.read for only the file path you are interested in.
Call the original implementation for other file paths.

Otherwise File.read calls from other parts of the codebase get stubbed incorrectly. You should use the stub_file_read, and expect_file_read helper methods which does the stubbing for File.read correctly.

# bad, all Files will read and return nothing
allow(File).to receive(:read)

# good
stub_file_read(my_filepath)

# also OK
allow(File).to receive(:read).and_call_original
allow(File).to receive(:read).with(my_filepath)

File system

File system data can be roughly split into "repositories", and "everything else". Repositories are stored in tmp/tests/repositories. This directory is emptied before a test run starts, and after the test run ends. It is not emptied between specs, so created repositories accumulate in this directory over the lifetime of the process. Deleting them is expensive, but this could lead to pollution unless carefully managed.

To avoid this, hashed storage is enabled in the test suite. This means that repositories are given a unique path that depends on their project's ID. Because the project IDs are not reset between specs, each spec gets its own repository on disk, and prevents changes from being visible between specs.

If a spec manually specifies a project ID, or inspects the state of the tmp/tests/repositories/ directory directly, then it should clean up the directory both before and after it runs. In general, these patterns should be completely avoided.

Other classes of file linked to database objects, such as uploads, are generally managed in the same way. With hashed storage enabled in the specs, they are written to disk in locations determined by ID, so conflicts should not occur.

Some specs disable hashed storage by passing the :legacy_storage trait to the projects factory. Specs that do this must never override the path of the project, or any of its groups. The default path includes the project ID, so it does not conflict. If two specs create a :legacy_storage project with the same path, they use the same repository on disk and lead to test environment pollution.

Other files must be managed manually by the spec. If you run code that creates a tmp/test-file.csv file, for instance, the spec must ensure that the file is removed as part of cleanup.

Persistent in-memory application state

All the specs in a given rspec run share the same Ruby process, which means they can affect each other by modifying Ruby objects that are accessible between specs. In practice, this means global variables, and constants (which includes Ruby classes, modules, etc).

Global variables should generally not be modified. If absolutely necessary, a block like this can be used to ensure the change is rolled back afterwards:

around(:each) do |example|
  old_value = $0

  begin
    $0 = "new-value"
    example.run
  ensure
    $0 = old_value
  end
end

If a spec needs to modify a constant, it should use the stub_const helper to ensure the change is rolled back.

If you need to modify the contents of the ENV constant, you can use the stub_env helper method instead.

While most Ruby instances are not shared between specs, classes and modules generally are. Class and module instance variables, accessors, class variables, and other stateful idioms, should be treated in the same way as global variables. Don't modify them unless you have to! In particular, prefer using expectations, or dependency injection along with stubs, to avoid the need for modifications. If you have no other choice, an around block like the global variables example can be used, but avoid this if at all possible.

Test Snowplow events

WARNING: Snowplow performs runtime type checks by using the contracts gem. Because Snowplow is by default disabled in tests and development, it can be hard to catch exceptions when mocking Gitlab::Tracking.

To catch runtime errors due to type checks, you can enable Snowplow in tests. Mark the spec with :snowplow and use the expect_snowplow_event helper, which checks for calls to Gitlab::Tracking#event.

describe '#show', :snowplow do
  it 'tracks snowplow events' do
    get :show

    expect_snowplow_event(
      category: 'Experiment',
      action: 'start',
      standard_context: { namespace: group, project: project }
    )
    expect_snowplow_event(
      category: 'Experiment',
      action: 'sent',
      property: 'property',
      label: 'label',
      standard_context: { namespace: group, project: project }
    )
  end
end

When you want to ensure that no event got called, you can use expect_no_snowplow_event.

  describe '#show', :snowplow do
    it 'does not track any snowplow events' do
      get :show

      expect_no_snowplow_event
    end
  end

Test Snowplow context against the schema

The Snowplow schema matcher helps to reduce validation errors by testing Snowplow context against the JSON schema. The schema matcher accepts the following parameters:

schema path
context

To add a schema matcher spec:

Add a new schema to the Iglu repository, then copy the same schema to the spec/fixtures/product_intelligence/ directory.
In the copied schema, remove the "$schema" key and value. We do not need it for specs and the spec fails if we keep the key, as it tries to look for the schema in the URL.

Use the following snippet to call the schema matcher:

match_snowplow_context_schema(schema_path: '<filename from step 1>', context: <Context Hash> )

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

  where(:a, :b, :result) do
    1         | 1        | true
    1         | 2        | false
    true      | true     | true
    true      | false    | 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

WARNING: Only use simple values as input in the where block. Using

procs, stateful

objects, FactoryBot-created objects, and similar items can lead to unexpected results.

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 (such as features or requests) but shouldn't be if they apply to multiple type of specs.

`be_like_time`

Time returned from a database can differ in precision from time objects in Ruby, so we need flexible tolerances when comparing in specs. We can use be_like_time to compare that times are within one second of each other.

Example:

expect(metrics.merged_at).to be_like_time(time)

`have_gitlab_http_status`

Prefer have_gitlab_http_status over have_http_status and expect(response.status).to 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.

Prefer named HTTP status like :no_content over its numeric representation 206. See a list of supported status codes.

Example:

expect(response).to have_gitlab_http_status(:ok)

`match_schema` and `match_response_schema`

The match_schema matcher allows validating that the subject matches a JSON schema. The item inside expect can be a JSON string or a JSON-compatible data structure.

match_response_schema is a convenience matcher for using with a response object. from a request spec.

Examples:

# Matches against spec/fixtures/api/schemas/prometheus/additional_metrics_query_result.json
expect(data).to match_schema('prometheus/additional_metrics_query_result')

# Matches against ee/spec/fixtures/api/schemas/board.json
expect(data).to match_schema('board', dir: 'ee')

# Matches against a schema made up of Ruby data structures
expect(data).to match_schema(Atlassian::Schemata.build_info)

`be_valid_json`

be_valid_json allows validating that a string parses as JSON and gives a non-empty result. To combine it with the schema matching above, use and:

expect(json_string).to be_valid_json

expect(json_string).to be_valid_json.and match_schema(schema)

Testing query performance

Testing query performance allows us to:

Assert that N+1 problems do not exist in a block of code.
Ensure that the number of queries in a block of code does not increase unnoticed.

QueryRecorder

QueryRecorder allows profiling and testing of the number of database queries performed in a given block of code.

See the QueryRecorder section for more details.

GitalyClient

Gitlab::GitalyClient.get_request_count allows tests of the number of Gitaly queries made by a given block of code:

See the Gitaly Request Counts section for more details.

Shared contexts

Shared contexts only used in one spec file can be declared inline. Any shared contexts used by more than one spec file:

Should be placed under spec/support/shared_contexts/.
Can be placed in subfolder if they apply to a certain type of specs only (such as features or requests) but shouldn't be if they apply to multiple type of specs.

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

Shared examples

Shared examples only used in one spec file can be declared inline. Any shared examples used by more than one spec file:

Should be placed under spec/support/shared_examples/.
Can be placed in subfolder if they apply to a certain type of specs only (such as features or requests) but shouldn't be if they apply to multiple type of specs.

Each file should include only one context and have a descriptive name, such as 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 placed under spec/support/helpers/. Helpers can be placed in a subfolder if they apply to a certain type of specs only (such as features or requests) 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 configuration. 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.
Prefer implicit or explicit association definitions instead of using create / build for association setup. See issue #262624 for further context.
Factories don't have to be limited to ActiveRecord objects. See example.
Factories and their traits should produce valid objects that are verified by specs.

Fixtures

All fixtures should be placed under spec/fixtures/.

Repositories

Testing some functionality, such as merging a merge request, requires a Git repository with a certain state to be present in the test environment. GitLab maintains the gitlab-test repository for certain common cases - you can ensure a copy of the repository is used with the :repository trait for project factories:

let(:project) { create(:project, :repository) }

Where you can, consider using the :custom_repo trait instead of :repository. This allows you to specify exactly what files appear in the master branch of the project's repository. For example:

let(:project) do
  create(
    :project, :custom_repo,
    files: {
      'README.md'       => 'Content here',
      'foo/bar/baz.txt' => 'More content here'
    }
  )
end

This creates a repository containing two files, with default permissions and the specified content.

Configuration

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

Each file should be related to a specific domain, such as spec/support/capybara.rb or spec/support/carrierwave.rb.

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 configuration 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.

Test environment logging

Services for the test environment are automatically configured and started when tests are run, including Gitaly, Workhorse, Elasticsearch, and Capybara. When run in CI, or if the service needs to be installed, the test environment logs information about set-up time, producing log messages like the following:

==> Setting up Gitaly...
    Gitaly set up in 31.459649 seconds...

==> Setting up GitLab Workhorse...
    GitLab Workhorse set up in 29.695619 seconds...
fatal: update refs/heads/diff-files-symlink-to-image: invalid <newvalue>: 8cfca84
From https://gitlab.com/gitlab-org/gitlab-test
 * [new branch]      diff-files-image-to-symlink -> origin/diff-files-image-to-symlink
 * [new branch]      diff-files-symlink-to-image -> origin/diff-files-symlink-to-image
 * [new branch]      diff-files-symlink-to-text -> origin/diff-files-symlink-to-text
 * [new branch]      diff-files-text-to-symlink -> origin/diff-files-text-to-symlink
   b80faa8..40232f7  snippet/multiple-files -> origin/snippet/multiple-files
 * [new branch]      testing/branch-with-#-hash -> origin/testing/branch-with-#-hash

==> Setting up GitLab Elasticsearch Indexer...
    GitLab Elasticsearch Indexer set up in 26.514623 seconds...

This information is omitted when running locally and when no action needs to be performed. If you would always like to see these messages, set the following environment variable:

GITLAB_TESTING_LOG_LEVEL=debug

Return to Testing documentation

Testing best practices

Test Design

RSpec

Ruby warnings

Test speed

Don't request capabilities you don't need

Optimize factory usage

Identify slow tests

Avoid repeating expensive actions

General guidelines

Coverage

System / Feature tests

UI testing

Actions

Finders

Matchers

Other useful methods

Live debug

Run :js spec in a visible browser

Screenshots

Fast unit tests

subject and let variables

Common test setup

Time-sensitive tests

Feature flags in tests

Pristine test environments

SQL database

Redis

Background jobs / Sidekiq

DNS

Stubbing File methods

File system

Persistent in-memory application state

Test Snowplow events

Test Snowplow context against the schema

Table-based / Parameterized tests

Prometheus tests

Matchers

be_like_time

have_gitlab_http_status

match_schema and match_response_schema

be_valid_json

Testing query performance

QueryRecorder

GitalyClient

Shared contexts

Shared examples

Helpers

Factories

Fixtures

Repositories

Configuration

Test environment logging

Run `:js` spec in a visible browser

`subject` and `let` variables

`be_like_time`

`have_gitlab_http_status`

`match_schema` and `match_response_schema`

`be_valid_json`