adds basic unit tests

src/amp-story-embed.js

@@ -92,6 +92,14 @@ export class AmpStoryEmbed {
     return this.element_;
   }
 
+  /**
+   * @visibleForTesting
+   * @return {!Element}
+   */
+  getRoot() {
+    return this.rootEl_;
+  }
+
   /** @public */
   buildCallback() {
     this.stories_ = toArray(this.element_.querySelectorAll('a'));
@@ -264,22 +272,33 @@ function layoutFallback(embedImpl) {
     setTimeout(() => {
       tick = true;
 
-      const embedTop = embedImpl.getElement()./*OK*/ getBoundingClientRect()
-        .top;
-      if (self./*OK*/ innerHeight * 2 > embedTop) {
-        embedImpl.layoutCallback();
-      }
+      layoutIfVisible(embedImpl);
     }, SCROLL_THROTTLE_MS);
 
     tick = false;
   });
+
+  // Calls it once it in case scroll event never fires.
+  layoutIfVisible(embedImpl);
+}
+
+/**
+ * Checks if embed is close to the viewport and calls layoutCallback when it is.
+ * @param {!AmpStoryEmbed} embedImpl
+ */
+function layoutIfVisible(embedImpl) {
+  const embedTop = embedImpl.getElement()./*OK*/ getBoundingClientRect().top;
+  if (self./*OK*/ innerHeight * 2 > embedTop) {
+    embedImpl.layoutCallback();
+  }
 }
 
 /**
  * Calls layoutCallback on the embed when it is close to the viewport.
  * @param {!AmpStoryEmbed} embedImpl
+ * @visibleForTesting
  */
-function layoutEmbed(embedImpl) {
+export function layoutEmbed(embedImpl) {
   if (IntersectionObserver && self === self.parent) {
     const intersectingCallback = entries => {
       entries.forEach(entry => {

test/unit/test-amp-story-embed.js

@@ -0,0 +1,72 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {AmpStoryEmbed, layoutEmbed} from '../../src/amp-story-embed';
+import {setStyles} from '../../src/style';
+
+describe('amp-story-embed', () => {
+  describes.realWin('AmpStoryEmbed', {amp: false}, env => {
+    let win;
+    let storyEmbed;
+    let embedEl;
+    let url;
+
+    function buildStoryEmbed() {
+      setStyles(win.document.body, {'width': '500px', 'height': '5500px'});
+      embedEl = win.document.createElement('amp-story-embed');
+      const storyAnchor = win.document.createElement('a');
+      url =
+        'https://www-washingtonpost-com.cdn.ampproject.org/v/s/www.washingtonpost.com/graphics/2019/lifestyle/travel/amp-stories/a-locals-guide-to-what-to-eat-and-do-in-new-york-city/?testParam=true';
+      storyAnchor.setAttribute('href', url);
+      embedEl.appendChild(storyAnchor);
+      storyEmbed = new AmpStoryEmbed(win, embedEl);
+      win.document.body.appendChild(embedEl);
+    }
+
+    beforeEach(() => {
+      win = env.win;
+      buildStoryEmbed();
+    });
+
+    it('should build an iframe for each story', () => {
+      storyEmbed.buildCallback();
+      layoutEmbed(storyEmbed);
+
+      const shadowRoot = storyEmbed.getRoot();
+      expect(shadowRoot.children.length).to.equal(1);
+    });
+
+    it('should correctly append params at the end of the story url', () => {
+      storyEmbed.buildCallback();
+      layoutEmbed(storyEmbed);
+
+      const shadowRoot = storyEmbed.getRoot();
+      expect(shadowRoot.firstElementChild.getAttribute('src')).to.equals(
+        url + '?amp_js_v=0.1#&visibilityState=inactive&origin=about%3Asrcdoc'
+      );
+    });
+
+    it('should correctly append params at the end of a story url with existing params', () => {
+      storyEmbed.buildCallback();
+      layoutEmbed(storyEmbed);
+
+      const shadowRoot = storyEmbed.getRoot();
+      expect(shadowRoot.firstElementChild.getAttribute('src')).to.equals(
+        url + '&amp_js_v=0.1#&visibilityState=inactive&origin=about%3Asrcdoc'
+      );
+    });
+  });
+});