Add test for when overriding default resolver

packages/jest-resolve/src/__mocks__/userResolver.js

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+*/
+
+'use strict';
+
+module.exports = function userResolver(path, options) {
+  return require('./module');
+};

packages/jest-resolve/src/__tests__/fixtures/module.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+*/
+
+'use strict';
+
+module.exports = 42;

packages/jest-resolve/src/__test__/resolve-test.js → packages/jest-resolve/src/__tests__/resolve-test.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+const path = require('path');
 const ModuleMap = require('jest-haste-map').ModuleMap;
 const Resolver = require('../');
 
@@ -37,3 +38,34 @@ describe('isCoreModule', () => {
     expect(isCore).toEqual(false);
   });
 });
+
+describe('findNodeModule', () => {
+  it('is possible to override the default resolver', () => {
+    const nodePaths = process.env.NODE_PATH
+      ? process.env.NODE_PATH.split(path.delimiter)
+      : null;
+
+    jest.mock('../__mocks__/userResolver');
+    const userResolver = require('../__mocks__/userResolver');
+    userResolver.mockImplementation(() => require('./fixtures/module'));
+
+    const newPath = Resolver.findNodeModule('test', {
+      basedir: '/',
+      browser: true,
+      extensions: ['js'],
+      moduleDirectory: ['node_modules'],
+      paths: ['/something'],
+      resolver: require.resolve('../__mocks__/userResolver'),
+    });
+
+    expect(newPath).toBe(require('./fixtures/module'));
+    expect(userResolver.mock.calls[0][0]).toBe('test');
+    expect(userResolver.mock.calls[0][1]).toEqual({
+      basedir: '/',
+      browser: true,
+      extensions: ['js'],
+      moduleDirectory: ['node_modules'],
+      paths: (nodePaths || []).concat(['/something']),
+    });
+  });
+});