chore: add --changedSince as MERGE_BASE to Jest in PR CI

Made-with: Cursor

Author: JoshuaKGoldberg

.github/workflows/frontend.yml

@@ -127,6 +127,10 @@ jobs:
     steps:
       - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
         name: Checkout sentry
+        with:
+          # PRs need history so we can compute merge base for Jest --changedSince.
+          # 100 is an arbitrary depth that will get most reasonable PRs' commits.
+          fetch-depth: ${{ github.event_name == 'pull_request' && '100' || '1' }}
 
       - uses: ./.github/actions/setup-node-pnpm
 
@@ -143,6 +147,26 @@ jobs:
           search_artifacts: true # Search for the last workflow run whose stored the artifact we're looking for
           if_no_artifact_found: warn # Can be one of: "fail", "warn", "ignore"
 
+      # On PRs, HEAD is the merge commit; its parents (HEAD^1, HEAD^2) are base and head.
+      # Merge base of those two is what Jest --changedSince needs. Checkout uses fetch-depth: 100 for PRs.
+      - name: Get merge base for changedSince (PRs only)
+        id: merge_base
+        if: github.event_name == 'pull_request'
+        run: |
+          MERGE_BASE=$(git merge-base HEAD^1 HEAD^2 2>/dev/null) || true
+          if [ -n "$MERGE_BASE" ]; then
+            CHANGED=$(git diff --name-only "$MERGE_BASE" HEAD)
+            if echo "$CHANGED" | grep -qv '/'; then
+              echo "Root-level file changed — running full test suite"
+              MERGE_BASE=""
+            else
+              echo "Merge base: $MERGE_BASE (Jest will use --changedSince)"
+            fi
+          else
+            echo "Merge base: could not compute, will run full test suite"
+          fi
+          echo "merge_base=${MERGE_BASE:-}" >> "$GITHUB_OUTPUT"
+
       - name: jest
         env:
           GITHUB_PR_SHA: ${{ github.event.pull_request.head.sha || github.sha }}
@@ -158,6 +182,7 @@ jobs:
           #
           # This quiets up the logs quite a bit.
           DEBUG_PRINT_LIMIT: 0
+          MERGE_BASE: ${{ steps.merge_base.outputs.merge_base }}
         run: pnpm run test-ci --forceExit
 
   form-field-registry:

eslint.config.ts

@@ -928,6 +928,7 @@ export default typescript.config([
     name: 'files/jest related',
     files: [
       'tests/js/jest-pegjs-transform.js',
+      'tests/js/sentry-test/jest-environment.js',
       'tests/js/sentry-test/mocks/*',
       'tests/js/sentry-test/loadFixtures.ts',
       'tests/js/setup.ts',

jest.config.ts

@@ -69,7 +69,18 @@ let JEST_TESTS: string[] | undefined;
 // to reexec itself here
 if (CI && !process.env.JEST_LIST_TESTS_INNER) {
   try {
-    const stdout = execFileSync('pnpm', ['exec', 'jest', '--listTests', '--json'], {
+    const listTestArguments = ['exec', 'jest', '--listTests', '--json'];
+
+    if (process.env.MERGE_BASE) {
+      console.log('MERGE_BASE detected:', process.env.MERGE_BASE);
+      listTestArguments.push(
+        '--changedSince',
+        process.env.MERGE_BASE,
+        '--passWithNoTests'
+      );
+    }
+
+    const stdout = execFileSync('pnpm', listTestArguments, {
       stdio: 'pipe',
       encoding: 'utf-8',
       env: {...process.env, JEST_LIST_TESTS_INNER: '1'},
@@ -108,6 +119,10 @@ function getTestsForGroup(
   allTests: ReadonlyArray<string>,
   testStats: Record<string, number>
 ): string[] {
+  if (allTests.length === 0) {
+    return [];
+  }
+
   const speculatedSuiteDuration = Object.values(testStats).reduce((a, b) => a + b, 0);
   const targetDuration = speculatedSuiteDuration / nodeTotal;
 
@@ -122,8 +137,13 @@ function getTestsForGroup(
   const tests = new Map<string, number>();
   const SUITE_P50_DURATION_MS = 1500;
 
+  const allTestsSet = new Set(allTests);
+
   // First, iterate over all of the tests we have stats for.
   Object.entries(testStats).forEach(([test, duration]) => {
+    if (!allTestsSet.has(test)) {
+      return;
+    }
     if (duration <= 0) {
       throw new Error(`Test duration is <= 0 for ${test}`);
     }
@@ -199,8 +219,8 @@ function getTestsForGroup(
     }
   }
 
-  if (!groups[nodeIndex]) {
-    throw new Error(`No tests found for node ${nodeIndex}`);
+  if (!groups[nodeIndex]?.length) {
+    return ['<rootDir>/__no_tests_for_this_shard__'];
   }
   return groups[nodeIndex].map(test => `<rootDir>/${test}`);
 }
@@ -285,6 +305,7 @@ const config: Config.InitialOptions = {
     // window/cookies state.
     '@sentry/toolbar': '<rootDir>/tests/js/sentry-test/mocks/sentryToolbarMock.js',
   },
+  passWithNoTests: !!process.env.MERGE_BASE,
   setupFiles: [
     '<rootDir>/static/app/utils/silence-react-unsafe-warnings.ts',
     'jest-canvas-mock',
@@ -333,8 +354,7 @@ const config: Config.InitialOptions = {
    */
   clearMocks: true,
 
-  // To disable the sentry jest integration, set this to 'jsdom'
-  testEnvironment: '@sentry/jest-environment/jsdom',
+  testEnvironment: '<rootDir>/tests/js/sentry-test/jest-environment.js',
   testEnvironmentOptions: {
     globalsCleanup: 'on',
     sentryConfig: {

tests/js/sentry-test/jest-environment.js

@@ -0,0 +1,28 @@
+const SentryEnvironment = require('@sentry/jest-environment/jsdom');
+
+// @sentry/jest-environment mutates config.projectConfig.testEnvironmentOptions
+// .sentryConfig.init in-place (pushing integrations and calling Sentry.init).
+// When Jest runs in-band (≤1 test, e.g. via --changedSince), those mutations
+// create circular references that crash ScriptTransformer's config serialisation.
+// Deep-cloning sentryConfig isolates the mutation from the original config object.
+class SafeSentryEnvironment extends SentryEnvironment {
+  /** @param {import('@jest/environment').JestEnvironmentConfig} config @param {import('@jest/environment').EnvironmentContext} context */
+  constructor(config, context) {
+    const sentryConfig = config.projectConfig.testEnvironmentOptions?.sentryConfig;
+    if (sentryConfig) {
+      config = {
+        ...config,
+        projectConfig: {
+          ...config.projectConfig,
+          testEnvironmentOptions: {
+            ...config.projectConfig.testEnvironmentOptions,
+            sentryConfig: structuredClone(sentryConfig),
+          },
+        },
+      };
+    }
+    super(config, context);
+  }
+}
+
+module.exports = SafeSentryEnvironment;

tests/js/sentry-test/sentry-jest-environment.d.ts

@@ -0,0 +1,7 @@
+declare module '@sentry/jest-environment/jsdom' {
+  // eslint-disable-next-line import/no-extraneous-dependencies -- transitive dep of jest
+  import type {JestEnvironment} from '@jest/environment';
+
+  const SentryEnvironment: typeof JestEnvironment;
+  export = SentryEnvironment;
+}