Overview of Frontend Testing

Tests relevant for frontend development can be found at the following places:

All tests in spec/javascripts/ will eventually be migrated to spec/frontend/ (see also #52483).

In addition there were feature tests in features/ run by Spinach in the past. These have been removed from our codebase in May 2018 (#23036).

See also:

Frontend unit tests

Unit tests are on the lowest abstraction level and typically test functionality that is not directly perceivable by a user.

When to use unit tests

exported functions and classes Anything that is exported can be reused at various places in a way you have no control over. Therefore it is necessary to document the expected behavior of the public interface with tests.
Vuex actions Any Vuex action needs to work in a consistent way independent of the component it is triggered from.
Vuex mutations For complex Vuex mutations it helps to identify the source of a problem by separating the tests from other parts of the Vuex store.

When not to use unit tests

non-exported functions or classes Anything that is not exported from a module can be considered private or an implementation detail and doesn't need to be tested.
constants Testing the value of a constant would mean to copy it. This results in extra effort without additional confidence that the value is correct.
Vue components Computed properties, methods, and lifecycle hooks can be considered an implementation detail of components and don't need to be tested. They are implicitly covered by component tests. The official Vue guidelines suggest the same.

What to mock in unit tests

state of the class under test Modifying the state of the class under test directly rather than using methods of the class avoids side-effects in test setup.
other exported classes Every class needs to be tested in isolation to prevent test scenarios from growing exponentially.
single DOM elements if passed as parameters For tests that only operate on single DOM elements rather than a whole page, creating these elements is cheaper than loading a whole HTML fixture.
all server requests When running frontend unit tests, the backend may not be reachable. Therefore all outgoing requests need to be mocked.
asynchronous background operations Background operations cannot be stopped or waited on, so they will continue running in the following tests and cause side effects.

What not to mock in unit tests

non-exported functions or classes Everything that is not exported can be considered private to the module and will be implicitly tested via the exported classes / functions.
methods of the class under test By mocking methods of the class under test, the mocks will be tested and not the real methods.
utility functions (pure functions, or those that only modify parameters) If a function has no side effects because it has no state, it is safe to not mock it in tests.
full HTML pages Loading the HTML of a full page slows down tests, so it should be avoided in unit tests.

Frontend component tests

Component tests cover the state of a single component that is perceivable by a user depending on external signals such as user input, events fired from other components, or application state.

When to use component tests

  • Vue components

When not to use component tests

Vue applications Vue applications may contain many components. Testing them on a component level requires too much effort. Therefore they are tested on frontend integration level.
HAML templates HAML templates contain only Markup and no frontend-side logic. Therefore they are not complete components.

What to mock in component tests

DOM Operating on the real DOM is significantly slower than on the virtual DOM.
properties and state of the component under test Similarly to testing classes, modifying the properties directly (rather than relying on methods of the component) avoids side-effects.
Vuex store To avoid side effects and keep component tests simple, Vuex stores are replaced with mocks.
all server requests Similar to unit tests, when running component tests, the backend may not be reachable. Therefore all outgoing requests need to be mocked.
asynchronous background operations Similar to unit tests, background operations cannot be stopped or waited on, so they will continue running in the following tests and cause side effects.
child components Every component is tested individually, so child components are mocked. See also shallowMount()

What not to mock in component tests

methods or computed properties of the component under test By mocking part of the component under test, the mocks will be tested and not the real component.
functions and classes independent from Vue All plain JavaScript code is already covered by unit tests and needs not to be mocked in component tests.

Frontend integration tests

Integration tests cover the interaction between all components on a single page. Their abstraction level is comparable to how a user would interact with the UI.

When to use integration tests

page bundles (index.js files in app/assets/javascripts/pages/) Testing the page bundles ensures the corresponding frontend components integrate well.
Vue applications outside of page bundles Testing Vue applications as a whole ensures the corresponding frontend components integrate well.

What to mock in integration tests

HAML views (use fixtures instead) Rendering HAML views requires a Rails environment including a running database which we cannot rely on in frontend tests.
all server requests Similar to unit and component tests, when running component tests, the backend may not be reachable. Therefore all outgoing requests need to be mocked.
asynchronous background operations that are not perceivable on the page Background operations that affect the page need to be tested on this level. All other background operations cannot be stopped or waited on, so they will continue running in the following tests and cause side effects.

What not to mock in integration tests

DOM Testing on the real DOM ensures our components work in the environment they are meant for. Part of this will be delegated to cross-browser testing.
properties or state of components On this level, all tests can only perform actions a user would do. For example to change the state of a component, a click event would be fired.
Vuex stores When testing the frontend code of a page as a whole, the interaction between Vue components and Vuex stores is covered as well.

Feature tests

In contrast to frontend integration tests, feature tests make requests against the real backend instead of using fixtures. This also implies that database queries are executed which makes this category significantly slower.

See also the RSpec testing guidelines.

When to use feature tests

  • use cases that require a backend and cannot be tested using fixtures
  • behavior that is not part of a page bundle but defined globally

Relevant notes

A :js flag is added to the test to make sure the full environment is loaded.

scenario 'successfully', :js do
  sign_in(create(:admin))
end

The steps of each test are written using capybara methods (documentation).

Bear in mind XHR calls might require you to use wait_for_requests in between steps, like so:

find('.form-control').native.send_keys(:enter)

wait_for_requests

expect(page).not_to have_selector('.card')

Test helpers

Vuex Helper: testAction

We have a helper available to make testing actions easier, as per official documentation:

testAction(
  actions.actionName, // action
  { }, // params to be passed to action
  state, // state
  [
    { type: types.MUTATION},
    { type: types.MUTATION_1, payload: {}},
  ], // mutations committed
  [
    { type: 'actionName', payload: {}},
    { type: 'actionName1', payload: {}},
  ] // actions dispatched
  done,
);

Check an example in spec/javascripts/ide/stores/actions_spec.jsspec/javascripts/ide/stores/actions_spec.js.

Vue Helper: mountComponent

To make mounting a Vue component easier and more readable, we have a few helpers available in spec/helpers/vue_mount_component_helper.

  • createComponentWithStore
  • mountComponentWithStore

Examples of usage:

beforeEach(() => {
  vm = createComponentWithStore(Component, store);

  vm.$store.state.currentBranchId = 'master';

  vm.$mount();
},
beforeEach(() => {
  vm = mountComponentWithStore(Component, {
    el: '#dummy-element',
    store,
    props: { badge },
  });
},

Don’t forget to clean up:

afterEach(() => {
  vm.$destroy();
});

Testing with older browsers

Some regressions only affect a specific browser version. We can install and test in particular browsers with either Firefox or Browserstack using the following steps:

Browserstack

Browserstack allows you to test more than 1200 mobile devices and browsers. You can use it directly through the live app or you can install the chrome extension for easy access. You can find the credentials on 1Password, under frontendteam@gitlab.com.

Firefox

macOS

You can download any older version of Firefox from the releases FTP server, https://ftp.mozilla.org/pub/firefox/releases/

  1. From the website, select a version, in this case 50.0.1.
  2. Go to the mac folder.
  3. Select your preferred language, you will find the dmg package inside, download it.
  4. Drag and drop the application to any other folder but the Applications folder.
  5. Rename the application to something like Firefox_Old.
  6. Move the application to the Applications folder.
  7. Open up a terminal and run /Applications/Firefox_Old.app/Contents/MacOS/firefox-bin -profilemanager to create a new profile specific to that Firefox version.
  8. Once the profile has been created, quit the app, and run it again like normal. You now have a working older Firefox version.