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Visual regression testing

Visual regression tests are split into two parts:

  1. The rendered UI (short: fixture)
  2. Instrumentation of that UI

Rendered UI

The composition of all tests happens in ./index.js. The rendered UI is either:

  1. located inside a separate file in ./fixtures and written as a React component.

    Here is an example with the Menu component.

  2. a demo from docs/data

    By default all demos are included. We exclude demos if they are redundant or flaky etc. The logic for this exclusion is handled (like the composition) in ./index.js

If you introduce new behavior, prefer adding a demo to the documentation to solve documentation and testing with one file. If you're adding a new test prefer a new component instead of editing existing files since that might unknowingly alter existing tests.

Instrumentation

Manual

yarn test:regressions:dev will build all fixtures and render an overview page that lists all fixtures. This can be used to debug individual fixtures. By default, a devtools-like view is shown that can be disabled by appending #no-dev to the URL e.g. http://localhost:3000/docs-customization-typography/CustomResponsiveFontSizes#no-dev or forced by appending #dev to the URL e.g. http://localhost:3000/docs-customization-typography/CustomResponsiveFontSizes#dev.

Automatic

We're using playwright to iterate over each fixture and take a screenshot. It allows catching regressions like this one:

before diff

Screenshots are saved in ./screenshots/$BROWSER_NAME/. Each test tests only a single fixture. A fixture can be loaded with await renderFixture(fixturePath) e.g. renderFixture('Unstable_TrapFocus/OpenTrapFocus').

Commands

For development yarn test:regressions:dev and yarn test:regressions:run --watch in separate terminals is recommended.

command description
yarn test:regressions Full run
yarn test:regressions:dev Prepares the fixtures to be able to test in watchmode
yarn test:regressions:run Runs the tests (requires yarn test:regressions:dev or yarn test:regressions:build+yarn test:regressions:server)
yarn test:regressions:build Builds the webpack bundle for viewing the fixtures
yarn test:regressions:server Serves the fixture bundle.