moduleNameMapper substitutions

Summary: Closes jestjs#839

Differential Revision: D3104032

fb-gh-sync-id: 9a251636d25ed0ff25a82d1cf281ac192e530624
fbshipit-source-id: 9a251636d25ed0ff25a82d1cf281ac192e530624

Author: Dmitrii Abramov

docs/API.md

@@ -420,11 +420,14 @@ A map from regular expressions to module names that allow to stub out resources,
 
 Use `<rootDir>` string token to refer to [`config.rootDir`](#config-rootdir-string) value if you want to use file paths.
 
+Additionally, you can substitute captured regex groups using numbered backreferences.
+
 Example:
 ```js
   "moduleNameMapper": {
     "^image![a-zA-Z0-9$_-]+$": "GlobalImageStub",
     "^[./a-zA-Z0-9$_-]+\.png$": "<rootDir>/RelativeImageStub.js",
+    "module_name_(.*)": "<rootDir>/substituted_module_$1.js"
   }
 ```
 

src/HasteModuleLoader/HasteModuleLoader.js

@@ -563,7 +563,7 @@ class Loader {
     for (const mappedModuleName in nameMapper) {
       const regex = nameMapper[mappedModuleName];
       if (regex.test(moduleName)) {
-        return mappedModuleName;
+        return moduleName.replace(regex, mappedModuleName);
       }
     }
   }

src/HasteModuleLoader/__tests__/HasteModuleLoader-requireModuleOrMock-test.js

@@ -30,6 +30,7 @@ describe('HasteModuleLoader', function() {
       '^image![a-zA-Z0-9$_-]+$': 'GlobalImageStub',
       '^[./a-zA-Z0-9$_-]+\.png$': 'RelativeImageStub',
       'mappedToPath': '<rootDir>/GlobalImageStub.js',
+      'module/name/(.*)': '<rootDir>/mapped_module_$1.js',
     },
   });
 
@@ -122,6 +123,9 @@ describe('HasteModuleLoader', function() {
 
         exports = loader.requireModuleOrMock(rootPath, 'dog.png');
         expect(exports.isRelativeImageStub).toBe(true);
+
+        exports = loader.requireModuleOrMock(rootPath, 'module/name/test');
+        expect(exports).toBe('mapped_module');
       });
     });
 

src/HasteModuleLoader/__tests__/test_root/mapped_module_test.js

@@ -0,0 +1,9 @@
+/**
+ * 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.
+ */
+
+module.exports = 'mapped_module';