Ensure proper handling of missing subtitle in content info banner

src/annotator/components/ContentInfoBanner.js

@@ -25,9 +25,10 @@ import {
  */
 export default function ContentInfoBanner({ info }) {
   // Format item title to show subtitle
-  const itemTitle = `${info.item.title}${info.item.subtitle && ': '}${
-    info.item.subtitle
-  }`;
+  let itemTitle = info.item.title;
+  if (info.item.subtitle) {
+    itemTitle += `: ${info.item.subtitle}`;
+  }
   return (
     <div
       className={classnames(

src/annotator/components/test/ContentInfoBanner-test.js

@@ -51,6 +51,15 @@ describe('ContentInfoBanner', () => {
     assert.equal(link.prop('target'), '_blank');
   });
 
+  it('handles missing subtitle', () => {
+    delete contentInfo.item.subtitle;
+
+    const wrapper = createComponent();
+
+    const link = wrapper.find('LinkUnstyled[data-testid="content-item-link"]');
+    assert.equal(link.text(), 'Chapter 2');
+  });
+
   it('provides disclosure of long titles through title attributes', () => {
     const wrapper = createComponent();