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Diffstat (limited to 'doc/development/testing_guide/frontend_testing.md')
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1 files changed, 17 insertions, 1 deletions
diff --git a/doc/development/testing_guide/frontend_testing.md b/doc/development/testing_guide/frontend_testing.md index 4c9d1684c00..28ebb6f0f64 100644 --- a/doc/development/testing_guide/frontend_testing.md +++ b/doc/development/testing_guide/frontend_testing.md @@ -27,14 +27,30 @@ we need to solve before being able to use Jest for all our needs. ### Differences to Karma - Jest runs in a Node.js environment, not in a browser. Support for running Jest tests in a browser [is planned](https://gitlab.com/gitlab-org/gitlab-ce/issues/58205). -- Because Jest runs in a Node.js environment, it uses [jsdom](https://github.com/jsdom/jsdom) by default. +- Because Jest runs in a Node.js environment, it uses [jsdom](https://github.com/jsdom/jsdom) by default. See also its [limitations](#limitations-of-jsdom) below. +- Jest does not have access to Webpack loaders or aliases. + The aliases used by Jest are defined in its [own config](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/jest.config.js). - All calls to `setTimeout` and `setInterval` are mocked away. See also [Jest Timer Mocks](https://jestjs.io/docs/en/timer-mocks). - `rewire` is not required because Jest supports mocking modules. See also [Manual Mocks](https://jestjs.io/docs/en/manual-mocks). +- No [context object](https://jasmine.github.io/tutorials/your_first_suite#section-The_%3Ccode%3Ethis%3C/code%3E_keyword) is passed to tests in Jest. + This means sharing `this.something` between `beforeEach()` and `it()` for example does not work. + Instead you should declare shared variables in the context that they are needed (via `const` / `let`). - The following will cause tests to fail in Jest: - Unmocked requests. - Unhandled Promise rejections. - Calls to `console.warn`, including warnings from libraries like Vue. +### Limitations of jsdom + +As mentioned [above](#differences-to-karma), Jest uses jsdom instead of a browser for running tests. +This comes with a number of limitations, namely: + +- [No scrolling support](https://github.com/jsdom/jsdom/blob/15.1.1/lib/jsdom/browser/Window.js#L623-L625) +- [No element sizes or positions](https://github.com/jsdom/jsdom/blob/15.1.1/lib/jsdom/living/nodes/Element-impl.js#L334-L371) +- [No layout engine](https://github.com/jsdom/jsdom/issues/1322) in general + +See also the issue for [support running Jest tests in browsers](https://gitlab.com/gitlab-org/gitlab-ce/issues/58205). + ### Debugging Jest tests Running `yarn jest-debug` will run Jest in debug mode, allowing you to debug/inspect as described in the [Jest docs](https://jestjs.io/docs/en/troubleshooting#tests-are-failing-and-you-don-t-know-why). |