feat(runtime): populate require.cache

packages/jest-runtime/src/__tests__/runtime_require_cache.test.js

@@ -0,0 +1,41 @@
+/**
+ * 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.
+ *
+ */
+
+'use strict';
+
+let createRuntime;
+
+describe('Runtime require.cache', () => {
+  beforeEach(() => {
+    createRuntime = require('createRuntime');
+  });
+
+  it('require.cache returns loaded module list as native Nodejs require does', () =>
+    createRuntime(__filename).then(runtime => {
+      const regularModule = runtime.requireModule(
+        runtime.__mockRootPath,
+        'RegularModule',
+      ).module;
+
+      expect(regularModule.require.cache[regularModule.id]).toBe(regularModule);
+    }));
+
+  it('require.cache is tolerant readonly', () =>
+    createRuntime(__filename).then(runtime => {
+      const regularModule = runtime.requireModule(
+        runtime.__mockRootPath,
+        'RegularModule',
+      ).module;
+
+      delete regularModule.require.cache[regularModule.id];
+      expect(regularModule.require.cache[regularModule.id]).toBe(regularModule);
+
+      regularModule.require.cache[regularModule.id] = 'something';
+      expect(regularModule.require.cache[regularModule.id]).toBe(regularModule);
+    }));
+});

packages/jest-runtime/src/index.ts

@@ -1238,19 +1238,49 @@ class Runtime {
     resolve.paths = (moduleName: string) =>
       this._requireResolvePaths(from.filename, moduleName);
 
+    const moduleRegistry = this._moduleRegistry;
+    const esmoduleRegistry = this._esmoduleRegistry;
     const moduleRequire = (options && options.isInternalModule
       ? (moduleName: string) =>
           this.requireInternalModule(from.filename, moduleName)
       : this.requireModuleOrMock.bind(
           this,
           from.filename,
         )) as LocalModuleRequire;
-    moduleRequire.cache = Object.create(null);
     moduleRequire.extensions = Object.create(null);
     moduleRequire.requireActual = this.requireActual.bind(this, from.filename);
     moduleRequire.requireMock = this.requireMock.bind(this, from.filename);
     moduleRequire.resolve = resolve;
 
+    Object.defineProperty(moduleRequire, 'cache', {
+      enumerable: true,
+      get() {
+        const cache: {[key: string]: any} = {};
+        const notPermittedMethod = () => {
+          console.warn('`require.cache` modification is not permitted');
+          return true;
+        };
+        moduleRegistry.forEach((value, key) => {
+          cache[key] = value;
+        });
+        esmoduleRegistry.forEach((value, key) => {
+          cache[key] = value;
+        });
+
+        return new Proxy(cache, {
+          defineProperty: notPermittedMethod,
+          deleteProperty: notPermittedMethod,
+          get(target, key) {
+            return typeof key === 'string' ? target[key] : undefined;
+          },
+          has(target, key) {
+            return typeof key === 'string' && !!target[key];
+          },
+          set: notPermittedMethod,
+        });
+      },
+    });
+
     Object.defineProperty(moduleRequire, 'main', {
       enumerable: true,
       get() {