MD Bookmarks: Proof-of-concept reimplementation of data storage/binding layer

chrome/test/data/webui/md_bookmarks/store_client_test.js

Index: chrome/test/data/webui/md_bookmarks/store_client_test.js
diff --git a/chrome/test/data/webui/md_bookmarks/store_client_test.js b/chrome/test/data/webui/md_bookmarks/store_client_test.js
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+++ b/chrome/test/data/webui/md_bookmarks/store_client_test.js
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+// Copyright 2017 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.
+
+suite('bookmarks.StoreClient', function() {
+  var store;
+  var client;
+
+  suiteSetup(function() {
+    document.body.innerHTML = `
+      <dom-module is="test-store-client">
+        <template>
+          <template is="dom-repeat" items="[[items]]">
+            <div class="item">[[item]]</div>
+          </template>
+        </template>
+      </dom-module>
+    `;
+
+    Polymer({
+      is: 'test-store-client',
+
+      behaviors: [bookmarks.StoreClient],
+
+      properties: {
+        items: {
+          type: Array,
+          observer: 'itemsChanged_',
+        },
+      },
+
+      attached: function() {
+        this.hasChanged = false;
+        this.observe('items', function(state) {
+          return state.items;
+        });
+        this.updateFromStore();
+      },
+
+      itemsChanged_: function(newItems, oldItems) {
+        if (oldItems)
+          this.hasChanged = true;
+      },
+    });
+  });
+
+  function update(newState) {
+    store.notifyObservers_(newState);
+    Polymer.dom.flush();
+  }
+
+  function getRenderedItems() {
+    return Array.from(client.root.querySelectorAll('.item'))
+        .map((div) => div.textContent.trim());
+  }
+
+  setup(function() {
+    PolymerTest.clearBody();
+
+    // Reset store instance:
+    bookmarks.Store.instance_ = new bookmarks.Store();
+    store = bookmarks.Store.getInstance();
+    store.init({
+      items: ['apple', 'banana', 'cantaloupe'],
+      count: 3,
+    });
+
+    client = document.createElement('test-store-client');
+    document.body.appendChild(client);
+    Polymer.dom.flush();
+  });
+
+  test('renders initial data', function() {
+    assertDeepEquals(['apple', 'banana', 'cantaloupe'], getRenderedItems());
+  });
+
+  test('renders changes to observed state', function() {
+    var newItems = ['apple', 'banana', 'courgette', 'durian'];
+    var newState = Object.assign({}, store.data, {
+      items: newItems,
+    });
+    update(newState);
+
+    assertTrue(client.hasChanged);
+    assertDeepEquals(newItems, getRenderedItems());
+  });
+
+  test('ignores changes to other subtrees', function() {
+    var newState = Object.assign({}, store.data, {count: 2});
+    update(newState);
+
+    assertFalse(client.hasChanged);
+  });
+});