Merge branch 'winh-yarn-test-command' into 'master'

Introduce yarn test to run Jest and Karma

See merge request gitlab-org/gitlab-ce!26320

doc/development/testing_guide/frontend_testing.md

@@ -225,14 +225,12 @@ See this [section][vue-test].
 
 ### Running frontend tests
 
-`rake karma` runs the frontend-only (JavaScript) tests.
-It consists of two subtasks:
+For running the frontend tests, you need the following commands:
 
-- `rake karma:fixtures` (re-)generates fixtures
-- `rake karma:tests` actually executes the tests
+- `rake karma:fixtures` (re-)generates fixtures.
+- `yarn test` executes the tests.
 
-As long as the fixtures don't change, `rake karma:tests` (or `yarn karma`)
-is sufficient (and saves you some time).
+As long as the fixtures don't change, `yarn test` is sufficient (and saves you some time).
 
 ### Live testing and focused testing
 

package.json

@@ -17,6 +17,7 @@
     "prettier-all": "node ./scripts/frontend/prettier.js check-all",
     "prettier-all-save": "node ./scripts/frontend/prettier.js save-all",
     "stylelint": "node node_modules/stylelint/bin/stylelint.js app/assets/stylesheets/**/*.* --custom-formatter node_modules/stylelint-error-string-formatter",
+    "test": "yarn jest && yarn karma",
     "webpack": "webpack --config config/webpack.config.js",
     "webpack-prod": "NODE_ENV=production webpack --config config/webpack.config.js"
   },