jestjs · SimenB · Jun 21, 2023 · Jun 8, 2023 · Jun 21, 2023 · Jun 21, 2023
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -17,6 +17,7 @@
 - `[jest-mock]` Improve user input validation and error messages of `spyOn` and `replaceProperty` methods ([#14087](https://github.com/facebook/jest/pull/14087))
 - `[jest-runtime]` Bind `jest.isolateModulesAsync` to `this` ([#14083](https://github.com/facebook/jest/pull/14083))
 - `[jest-runtime]` Forward `wrapperLength` to the `Script` constructor as `columnOffset` for accurate debugging ([#14148](https://github.com/facebook/jest/pull/14148))
+- `[jest-runtime]` Guard `_isMockFunction` access with `in` ([#14188](https://github.com/facebook/jest/pull/14188))
 - `[jest-snapshot]` Fix a potential bug when not using prettier and improve performance ([#14036](https://github.com/facebook/jest/pull/14036))
 - `[@jest/transform]` Do not instrument `.json` modules ([#14048](https://github.com/facebook/jest/pull/14048))
 

diff --git a/packages/jest-runtime/src/__tests__/runtime_resetModules_unsafe_global_proxy.js b/packages/jest-runtime/src/__tests__/runtime_resetModules_unsafe_global_proxy.js
@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
+'use strict';
+
+let createRuntime;
+
+describe('Runtime', () => {
+  beforeEach(() => {
+    createRuntime = require('createRuntime');
+  });
+
+  describe('resetModules', () => {
+    it('does not throw when accessing _isMockFunction on an unsafe global', async () => {
+      const runtime = await createRuntime(__filename);
+      runtime._environment.global.UNSAFE_GLOBAL = new Proxy(
+        {},
+        {
+          get(target, p, receiver) {
+            if (p === '_isMockFunction') throw new Error('Unsafe global!');
+          },
+        },
+      );
+      expect(() => runtime.resetModules()).not.toThrow();
+    });
+  });
+});
diff --git a/packages/jest-runtime/src/index.ts b/packages/jest-runtime/src/index.ts
@@ -1218,6 +1218,7 @@ export default class Runtime {
             if (
               ((typeof globalMock === 'object' && globalMock !== null) ||
                 typeof globalMock === 'function') &&
+              '_isMockFunction' in globalMock &&
               globalMock._isMockFunction === true
             ) {
               globalMock.mockClear();