Bust jest caching and fix tests

react-packager/src/Cache/__mocks__/Cache.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2015-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';
+
+class Cache {
+  get(filepath, field, cb) {
+    return cb(filepath);
+  }
+
+  invalidate(filepath) { }
+  end() { }
+}
+
+module.exports = Cache;

react-packager/src/Cache/__tests__/Cache-test.js

@@ -52,6 +52,14 @@ describe('JSTransformer Cache', () => {
     });
 
     pit('supports storing multiple fields', () => {
+      require('fs').stat.mockImpl((file, callback) => {
+        callback(null, {
+          mtime: {
+            getTime: () => {}
+          }
+        });
+      });
+
       var cache = new Cache({
         projectRoots: ['/rootDir'],
         transformModulePath: 'x.js',