Introduce jest minimal jobs

jest minimal jobs runs jest with --findRelatedTests
on the files that changed in the merge request

The jobs generally will run before an MR approval, except
when the MR contains the following changes:

  - "{package.json,yarn.lock}"
  - "babel.config.js"
  - "jest.config.{base,integration,unit}.js"
  - "vendor/assets/javascripts/**/*"
  - "{,ee}/app/assets/**/*.graphql"
  - "config/helpers/**/*.js"

The full jest pipeline could also be triggered
using a MR label pipeline:run-all-jest

.gitlab/ci/frontend.gitlab-ci.yml

@@ -188,13 +188,14 @@ eslint-as-if-foss:
 .jest-base:
   extends: .frontend-test-base
   script:
-    - run_timed_command "yarn jest --ci --coverage --testSequencer ./scripts/frontend/parallel_ci_sequencer.js"
+    - run_timed_command "yarn jest:ci"
 
 jest:
   extends:
     - .jest-base
-    - .frontend:rules:default-frontend-jobs
+    - .frontend:rules:jest
   needs:
+    - job: "detect-tests"
     - job: "rspec frontend_fixture"
     - job: "rspec-ee frontend_fixture"
       optional: true
@@ -210,6 +211,13 @@ jest:
       junit: junit_jest.xml
   parallel: 5
 
+jest minimal:
+  extends:
+    - jest
+    - .frontend:rules:jest:minimal
+  script:
+    - run_timed_command "yarn jest:ci:minimal"
+
 jest-integration:
   extends:
     - .frontend-test-base
@@ -235,7 +243,11 @@ coverage-frontend:
     - .default-retry
     - .yarn-cache
     - .frontend:rules:ee-mr-and-default-branch-only
-  needs: ["jest"]
+  needs:
+    - job: "jest"
+      optional: true
+    - job: "jest minimal"
+      optional: true
   stage: post-test
   before_script:
     - *yarn-install

.gitlab/ci/rules.gitlab-ci.yml

@@ -46,6 +46,9 @@
 .if-merge-request-title-run-all-rspec: &if-merge-request-title-run-all-rspec
   if: '$CI_MERGE_REQUEST_LABELS =~ /pipeline:run-all-rspec/'
 
+.if-merge-request-title-run-all-jest: &if-merge-request-title-run-all-jest
+  if: '$CI_MERGE_REQUEST_LABELS =~ /pipeline:run-all-jest/'
+
 .if-merge-request-run-decomposed: &if-merge-request-run-decomposed
   if: '$CI_MERGE_REQUEST_LABELS =~ /pipeline:run-decomposed/'
 
@@ -365,6 +368,14 @@
   - "danger/**/*"
   - "tooling/danger/**/*"
 
+.core-frontend-patterns: &core-frontend-patterns
+  - "{package.json,yarn.lock}"
+  - "babel.config.js"
+  - "jest.config.{base,integration,unit}.js"
+  - "config/helpers/**/*.js"
+  - "vendor/assets/javascripts/**/*"
+  - "{,ee}/app/assets/**/*.graphql"
+
 ################
 # Shared rules #
 ################
@@ -525,6 +536,37 @@
     - <<: *if-merge-request
       changes: *ci-patterns
 
+.frontend:rules:jest:
+  rules:
+    - <<: *if-merge-request-title-run-all-jest
+    - <<: *if-default-refs
+      changes: *core-frontend-patterns
+    - <<: *if-merge-request
+      changes: *ci-patterns
+    - <<: *if-automated-merge-request
+      changes: *code-backstage-patterns
+    - <<: *if-merge-request-not-approved
+      when: never
+    - <<: *if-default-refs
+      changes: *code-backstage-patterns
+
+.frontend:rules:jest:minimal:
+  rules:
+    - <<: *if-merge-request-approved
+      when: never
+    - <<: *if-automated-merge-request
+      when: never
+    - <<: *if-merge-request-title-run-all-jest
+      when: never
+    - <<: *if-default-refs
+      changes: *core-frontend-patterns
+      when: never
+    - <<: *if-merge-request
+      changes: *ci-patterns
+      when: never
+    - <<: *if-merge-request
+      changes: *code-backstage-patterns
+
 .frontend:rules:eslint-as-if-foss:
   rules:
     - <<: *if-not-ee

.gitlab/ci/setup.gitlab-ci.yml

@@ -70,9 +70,12 @@ verify-tests-yml:
     - install_gitlab_gem
     - install_tff_gem
     - retrieve_tests_mapping
-    - 'if [ -n "$CI_MERGE_REQUEST_IID" ]; then tooling/bin/find_changes ${CHANGES_FILE}; fi'
-    - 'if [ -n "$CI_MERGE_REQUEST_IID" ]; then tooling/bin/find_tests ${CHANGES_FILE} ${MATCHED_TESTS_FILE}; fi'
-    - 'if [ -n "$CI_MERGE_REQUEST_IID" ]; then echo "related rspec tests: $(cat $MATCHED_TESTS_FILE)"; fi'
+    - |
+      if [ -n "$CI_MERGE_REQUEST_IID" ]; then
+        tooling/bin/find_changes ${CHANGES_FILE};
+        tooling/bin/find_tests ${CHANGES_FILE} ${MATCHED_TESTS_FILE};
+        echo "related rspec tests: $(cat $MATCHED_TESTS_FILE)";
+      fi
   artifacts:
     expire_in: 7d
     paths:

package.json

@@ -13,6 +13,8 @@
     "prejest": "yarn check-dependencies",
     "jest": "jest --config jest.config.js",
     "jest-debug": "node --inspect-brk node_modules/.bin/jest --runInBand",
+    "jest:ci": "jest --config jest.config.js --ci --coverage --testSequencer ./scripts/frontend/parallel_ci_sequencer.js",
+    "jest:ci:minimal": "jest --config jest.config.js --ci --coverage --findRelatedTests $(cat tmp/changed_files.txt) --passWithNoTests --testSequencer ./scripts/frontend/parallel_ci_sequencer.js",
     "jest:integration": "jest --config jest.config.integration.js",
     "jsdoc": "jsdoc -c config/jsdocs.config.js",
     "lint:eslint": "yarn run internal:eslint",