Properly resolve mocked node modules without package.json defined

CHANGELOG.md

@@ -168,6 +168,8 @@
   regardless of order ([#6150](https://github.com/facebook/jest/pull/6150))
 * `[pretty-format]` [**BREAKING**] Remove undefined props from React elements
   ([#6162](https://github.com/facebook/jest/pull/6162))
+* `[jest-haste-map]` Properly resolve mocked node modules without package.json
+  defined ([#6232](https://github.com/facebook/jest/pull/6232))
 
 ### Chore & Maintenance
 

integration-tests/resolve-node-module/__mocks__/mock-module-without-pkg/index.js

@@ -0,0 +1,8 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ */
+
+module.exports = 'test mock-module-without-pkg';

integration-tests/resolve-node-module/__tests__/resolve-node-module.test.js

@@ -10,6 +10,7 @@
 jest.mock('mock-module');
 jest.mock('mock-module-alt');
 jest.mock('mock-jsx-module');
+jest.mock('mock-module-without-pkg');
 
 it('should resolve entry as index.js when package main is "."', () => {
   const mockModule = require('mock-module');
@@ -25,3 +26,8 @@ it('should resolve entry as index with other configured module file extension wh
   const mockJsxModule = require('mock-jsx-module');
   expect(mockJsxModule).toEqual('test jsx');
 });
+
+it('should resolve entry as index without package.json', () => {
+  const mockModuleWithoutPkg = require('mock-module-without-pkg');
+  expect(mockModuleWithoutPkg).toEqual('test mock-module-without-pkg');
+});

packages/jest-haste-map/src/module_map.js

@@ -56,7 +56,7 @@ export default class ModuleMap {
   }
 
   getMockModule(name: string): ?Path {
-    return this._raw.mocks[name];
+    return this._raw.mocks[name] || this._raw.mocks[name + '/index'];
   }
 
   getRawModuleMap(): RawModuleMap {