Add an unittest for background/volume_manager.js

chrome/test/data/file_manager/unit_tests/test_util.js

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * Invokes a callback function depending on the result of promise.
+ *
+ * @param {Promise} promise Promise.
+ * @param {function(boolean)} calllback Callback function. True is passed if the
+ *     test failed.
+ */
+function reportPromise(promise, callback) {
+  promise.then(function() {
+    callback(/* error */ false);
+  }, function(error) {
+    console.error(error.stack || error);
+    callback(/* error */ true);
+  });
+}