fix(jest): scope coverage output per-project in multi-project workspaces (fixes #1009)

packages/jest/src/default-config.resolver.ts

@@ -1,5 +1,6 @@
 import { pick } from 'lodash';
 import { getSystemPath, normalize, Path } from '@angular-devkit/core';
+import * as path from 'node:path';
 
 import { JestConfig } from './types';
 import { getTsConfigPath } from './utils';
@@ -39,6 +40,9 @@ export class DefaultConfigResolver {
   resolveForProject(projectRoot: Path): JestConfig {
     return {
       testMatch: [`${getSystemPath(projectRoot)}${testPattern}`],
+      // Scope coverage output to the project directory so that multiple projects
+      // in a workspace don't overwrite each other's coverage reports. See #1009.
+      coverageDirectory: path.join(getSystemPath(projectRoot), 'coverage'),
       transform: {
         [this.tsJestTransformRegExp]: [
           'jest-preset-angular',

packages/jest/tests/integration.js

@@ -107,6 +107,15 @@ module.exports = [
       'node ../../../packages/jest/tests/validate.js my-shared-library --find-related-tests projects/my-shared-library/src/lib/my-shared-library.service.ts projects/my-shared-library/src/lib/my-shared-library.component.ts --expect-suites=2 --expect-tests=2',
   },
 
+  {
+    id: 'multi-project-coverage',
+    name: 'jest: multi-project coverage scoping',
+    purpose: 'Coverage output is scoped per project, not overwritten',
+    app: 'examples/jest/multiple-apps',
+    command:
+      'node ../../../packages/jest/tests/validate-coverage.js',
+  },
+
   // E2E sanity
   {
     id: 'e2e-simple-app',

packages/jest/tests/validate-coverage.js

@@ -0,0 +1,49 @@
+#!/usr/bin/env node
+/**
+ * Validates that coverage output is scoped per Angular project (fixes #1009).
+ *
+ * Each project should write coverage to <projectRoot>/coverage/, not to a shared
+ * root-level directory that gets overwritten when multiple projects run.
+ *
+ * Run from the multiple-apps example directory.
+ */
+const { execSync } = require('child_process');
+const fs = require('fs');
+const path = require('path');
+
+const projects = ['my-first-app', 'my-second-app', 'my-shared-library'];
+const cwd = process.cwd();
+let allPassed = true;
+
+for (const project of projects) {
+  console.log(`\nRunning: ng test ${project} --coverage`);
+  try {
+    execSync(`yarn test ${project} --coverage 2>&1`, { encoding: 'utf-8', stdio: 'pipe' });
+  } catch (e) {
+    // Jest exits non-zero on test failure but still writes coverage; ignore for this check
+  }
+
+  // Angular CLI project root is under `projects/<name>`
+  const projectRoot = path.join(cwd, 'projects', project);
+  const coverageDir = path.join(projectRoot, 'coverage');
+
+  if (!fs.existsSync(coverageDir)) {
+    console.error(`FAIL: Expected coverage directory not found: ${coverageDir}`);
+    console.error(`      (coverage was likely written to root ./coverage instead)`);
+    allPassed = false;
+  } else {
+    console.log(`OK: Coverage scoped correctly at ${coverageDir}`);
+  }
+}
+
+// Also assert that no root-level coverage dir was created (it would indicate the fix didn't work)
+const rootCoverageDir = path.join(cwd, 'coverage');
+if (fs.existsSync(rootCoverageDir)) {
+  console.warn(`WARN: Root-level coverage/ directory exists at ${rootCoverageDir}`);
+  console.warn(`      This may indicate per-project scoping is not fully working.`);
+}
+
+if (!allPassed) {
+  process.exit(1);
+}
+console.log('\nAll per-project coverage directories verified correctly.');