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
andspy
are faster thanFactoryBot.build(...)
-
FactoryBot.build(...)
and.build_stubbed
are faster than.create
. - Don't
create
an object whenbuild
,build_stubbed
,attributes_for
,spy
, ordouble
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
andafter
hooks, prefer it scoped to:context
over:all
- When using
evaluate_script("$('.js-foo').testSomething()")
(orexecute_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: Note: Before writing a new system test, please consider not writing one!
- Feature specs should be named
ROLE_ACTION_spec.rb
, such asuser_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.
:js
spec in a visible browser
Run 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.
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 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 tolet
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'sit
block. - Don't define a
let
variable inside the top-leveldescribe
block that's only used in a more deeply-nestedcontext
ordescribe
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 inusers.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 ofFactoryBot.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.