fix: properly return mocks when using jest.isolatedModules (#11882)

Author: SimenB

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Fixes
 
+- `[jest-runtime]` Fix regression when using `jest.isolateModules` and mocks ([#11882](https://github.com/facebook/jest/pull/11882))
+
 ### Chore & Maintenance
 
 ### Performance

e2e/__tests__/isolateModules.test.ts

@@ -0,0 +1,55 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {tmpdir} from 'os';
+import * as path from 'path';
+import {cleanup, createEmptyPackage, writeFiles} from '../Utils';
+import runJest from '../runJest';
+
+const DIR = path.resolve(tmpdir(), 'isolate-modules.test');
+
+beforeEach(() => {
+  cleanup(DIR);
+  createEmptyPackage(DIR);
+});
+
+afterAll(() => cleanup(DIR));
+
+test('works with mocks', () => {
+  writeFiles(DIR, {
+    'config.js': `
+      module.exports.getBoolean = function getBoolean(variableName) {
+        return false;
+      }
+    `,
+    'read.js': `
+      const {getBoolean} = require('./config');
+
+      const value = getBoolean('foo');
+      console.log("was " + value);
+    `,
+    'test.js': `
+      jest.mock('./config');
+      const config = require('./config');
+
+      test('dummy test', () => {
+        const configGetMock = config.getBoolean.mockImplementation(() => {
+          return true;
+        });
+
+        jest.isolateModules(() => {
+          require("./read");
+        });
+
+        expect(configGetMock).toBeCalledTimes(1);
+      })
+    `,
+  });
+  const {exitCode} = runJest(DIR);
+
+  expect(exitCode).toBe(0);
+});

packages/jest-runtime/src/index.ts

@@ -861,12 +861,14 @@ export default class Runtime {
       {conditions: this.cjsConditions},
     );
 
-    const mockRegistry = this._isolatedMockRegistry || this._mockRegistry;
-
-    if (mockRegistry.get(moduleID)) {
-      return mockRegistry.get(moduleID);
+    if (this._isolatedMockRegistry?.has(moduleID)) {
+      return this._isolatedMockRegistry.get(moduleID);
+    } else if (this._mockRegistry.has(moduleID)) {
+      return this._mockRegistry.get(moduleID);
     }
 
+    const mockRegistry = this._isolatedMockRegistry || this._mockRegistry;
+
     if (this._mockFactories.has(moduleID)) {
       // has check above makes this ok
       const module = this._mockFactories.get(moduleID)!();