debian-mirror-gitlab/doc/development/testing_guide/testing_levels.md

# Testing levels

![Testing priority triangle](img/testing_triangle.png)

_This diagram demonstrates the relative priority of each test type we use. `e2e` stands for end-to-end._

## Unit tests

Formal definition: <https://en.wikipedia.org/wiki/Unit_testing>

These kind of tests ensure that a single unit of code (a method) works as
expected (given an input, it has a predictable output). These tests should be
isolated as much as possible. For example, model methods that don't do anything
with the database shouldn't need a DB record. Classes that don't need database
records should use stubs/doubles as much as possible.

| Code path | Tests path | Testing engine | Notes |
| --------- | ---------- | -------------- | ----- |
| `app/finders/` | `spec/finders/` | RSpec | |
| `app/helpers/` | `spec/helpers/` | RSpec | |
| `app/db/{post_,}migrate/` | `spec/migrations/` | RSpec | More details at [`spec/migrations/README.md`](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/spec/migrations/README.md). |
| `app/policies/` | `spec/policies/` | RSpec | |
| `app/presenters/` | `spec/presenters/` | RSpec | |
| `app/routing/` | `spec/routing/` | RSpec | |
| `app/serializers/` | `spec/serializers/` | RSpec | |
| `app/services/` | `spec/services/` | RSpec | |
| `app/tasks/` | `spec/tasks/` | RSpec | |
| `app/uploaders/` | `spec/uploaders/` | RSpec | |
| `app/views/` | `spec/views/` | RSpec | |
| `app/workers/` | `spec/workers/` | RSpec | |
| `app/assets/javascripts/` | `spec/javascripts/` | Karma | More details in the [Frontend Testing guide](frontend_testing.md) section. |

## Integration tests

Formal definition: <https://en.wikipedia.org/wiki/Integration_testing>

These kind of tests ensure that individual parts of the application work well
together, without the overhead of the actual app environment (i.e. the browser).
These tests should assert at the request/response level: status code, headers,
body.
They're useful to test permissions, redirections, what view is rendered etc.

| Code path | Tests path | Testing engine | Notes |
| --------- | ---------- | -------------- | ----- |
| `app/controllers/` | `spec/controllers/` | RSpec | |
| `app/mailers/` | `spec/mailers/` | RSpec | |
| `lib/api/` | `spec/requests/api/` | RSpec | |
| `lib/ci/api/` | `spec/requests/ci/api/` | RSpec | |
| `app/assets/javascripts/` | `spec/javascripts/` | Karma | More details in the [JavaScript](#javascript) section. |

### About controller tests

In an ideal world, controllers should be thin. However, when this is not the
case, it's acceptable to write a system/feature test without JavaScript instead
of a controller test. The reason is that testing a fat controller usually
involves a lot of stubbing, things like:

```ruby
controller.instance_variable_set(:@user, user)
```

and use methods which are deprecated in Rails 5 ([#23768]).

[#23768]: https://gitlab.com/gitlab-org/gitlab-ce/issues/23768

### About Karma

As you may have noticed, Karma is both in the Unit tests and the Integration
tests category. That's because Karma is a tool that provides an environment to
run JavaScript tests, so you can either run unit tests (e.g. test a single
JavaScript method), or integration tests (e.g. test a component that is composed
of multiple components).

## White-box tests at the system level (formerly known as System / Feature tests)

Formal definitions:

- <https://en.wikipedia.org/wiki/System_testing>
- <https://en.wikipedia.org/wiki/White-box_testing>

These kind of tests ensure the GitLab *Rails* application (i.e.
`gitlab-ce`/`gitlab-ee`) works as expected from a *browser* point of view.

Note that:

- knowledge of the internals of the application are still required
- data needed for the tests are usually created directly using RSpec factories
- expectations are often set on the database or objects state

These tests should only be used when:

- the functionality/component being tested is small
- the internal state of the objects/database *needs* to be tested
- it cannot be tested at a lower level

For instance, to test the breadcrumbs on a given page, writing a system test
makes sense since it's a small component, which cannot be tested at the unit or
controller level.

Only test the happy path, but make sure to add a test case for any regression
that couldn't have been caught at lower levels with better tests (i.e. if a
regression is found, regression tests should be added at the lowest-level
possible).

| Tests path | Testing engine | Notes |
| ---------- | -------------- | ----- |
| `spec/features/` | [Capybara] + [RSpec] | If your test has the `:js` metadata, the browser driver will be [Poltergeist], otherwise it's using [RackTest]. |

### Consider **not** writing a system test!

If we're confident that the low-level components work well (and we should be if
we have enough Unit & Integration tests), we shouldn't need to duplicate their
thorough testing at the System test level.

It's very easy to add tests, but a lot harder to remove or improve tests, so one
should take care of not introducing too many (slow and duplicated) tests.

The reasons why we should follow these best practices are as follows:

- System tests are slow to run since they spin up the entire application stack
  in a headless browser, and even slower when they integrate a JS driver
- When system tests run with a JavaScript driver, the tests are run in a
  different thread than the application. This means it does not share a
  database connection and your test will have to commit the transactions in
  order for the running application to see the data (and vice-versa). In that
  case we need to truncate the database after each spec instead of simply
  rolling back a transaction (the faster strategy that's in use for other kind
  of tests). This is slower than transactions, however, so we want to use
  truncation only when necessary.

[Poltergeist]: https://github.com/teamcapybara/capybara#poltergeist
[RackTest]: https://github.com/teamcapybara/capybara#racktest

## Black-box tests at the system level, aka end-to-end tests

Formal definitions:

- <https://en.wikipedia.org/wiki/System_testing>
- <https://en.wikipedia.org/wiki/Black-box_testing>

GitLab consists of [multiple pieces] such as [GitLab Shell], [GitLab Workhorse],
[Gitaly], [GitLab Pages], [GitLab Runner], and GitLab Rails. All theses pieces
are configured and packaged by [GitLab Omnibus].

The QA framework and instance-level scenarios are [part of GitLab Rails] so that
they're always in-sync with the codebase (especially the views).

Note that:

- knowledge of the internals of the application are not required
- data needed for the tests can only be created using the GUI or the API
- expectations can only be made against the browser page and API responses

Every new feature should come with a [test plan].

| Tests path | Testing engine | Notes |
| ---------- | -------------- | ----- |
| `qa/qa/specs/features/` | [Capybara] + [RSpec] + Custom QA framework | Tests should be placed under their corresponding [Product category] |

> See [end-to-end tests](end_to_end_tests.md) for more information.

[multiple pieces]: ../architecture.md#components
[GitLab Shell]: https://gitlab.com/gitlab-org/gitlab-shell
[GitLab Workhorse]: https://gitlab.com/gitlab-org/gitlab-workhorse
[Gitaly]: https://gitlab.com/gitlab-org/gitaly
[GitLab Pages]: https://gitlab.com/gitlab-org/gitlab-pages
[GitLab Runner]: https://gitlab.com/gitlab-org/gitlab-runner
[GitLab Omnibus]: https://gitlab.com/gitlab-org/omnibus-gitlab
[part of GitLab Rails]: https://gitlab.com/gitlab-org/gitlab-ce/tree/master/qa
[test plan]: https://gitlab.com/gitlab-org/gitlab-ce/tree/master/.gitlab/issue_templates/Test%20plan.md
[Product category]: https://about.gitlab.com/handbook/product/categories/

### Smoke tests

Smoke tests are quick tests that may be run at any time (especially after the
pre-deployment migrations).

These tests run against the UI and ensure that basic functionality is working.

> See [Smoke Tests](smoke.md) for more information.

### GitLab QA orchestrator

[GitLab QA orchestrator] is a tool that allows to test that all these pieces
integrate well together by building a Docker image for a given version of GitLab
Rails and running end-to-end tests (i.e. using Capybara) against it.

Learn more in the [GitLab QA orchestrator README][gitlab-qa-readme].

[GitLab QA orchestrator]: https://gitlab.com/gitlab-org/gitlab-qa
[gitlab-qa-readme]: https://gitlab.com/gitlab-org/gitlab-qa/tree/master/README.md

## EE-specific tests

EE-specific tests follows the same organization, but under the `ee/spec` folder.

## How to test at the correct level?

As many things in life, deciding what to test at each level of testing is a
trade-off:

- Unit tests are usually cheap, and you should consider them like the basement
  of your house: you need them to be confident that your code is behaving
  correctly. However if you run only unit tests without integration / system
  tests, you might [miss] the [big] / [picture] !
- Integration tests are a bit more expensive, but don't abuse them. A system test
  is often better than an integration test that is stubbing a lot of internals.
- System tests are expensive (compared to unit tests), even more if they require
  a JavaScript driver. Make sure to follow the guidelines in the [Speed](#test-speed)
  section.

Another way to see it is to think about the "cost of tests", this is well
explained [in this article][tests-cost] and the basic idea is that the cost of a
test includes:

- The time it takes to write the test
- The time it takes to run the test every time the suite runs
- The time it takes to understand the test
- The time it takes to fix the test if it breaks and the underlying code is OK
- Maybe, the time it takes to change the code to make the code testable.

### Frontend-related tests

There are cases where the behaviour you are testing is not worth the time spent
running the full application, for example, if you are testing styling, animation,
edge cases or small actions that don't involve the backend,
you should write an integration test using Jasmine.

[miss]: https://twitter.com/ThePracticalDev/status/850748070698651649
[big]: https://twitter.com/timbray/status/822470746773409794
[picture]: https://twitter.com/withzombies/status/829716565834752000
[tests-cost]: https://medium.com/table-xi/high-cost-tests-and-high-value-tests-a86e27a54df#.2ulyh3a4e

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