Add test to check `describe` fails when selection spans multiple pages

src/annotator/anchoring/test/fake-pdf-viewer-application.js

@@ -108,16 +108,18 @@ function createPage(content, rendered) {
 /**
  * Set the index of the page which is currently visible in the viewport.
  *
- * The page which is visible will be "rendered" and have a text layer available.
- * For other pages, there will only be a placeholder element for the whole page.
+ * Pages from `index` up to and including `lastRenderedPage` will be
+ * "rendered" and have a text layer available. Other pages will be "un-rendered"
+ * with no text layer available, but only a placeholder element for the whole
+ * page.
  */
-FakePDFViewerApplication.prototype.setCurrentPage = function (index) {
+FakePDFViewerApplication.prototype.setCurrentPage = function (index, lastRenderedPage=index) {
   const self = this;
 
   this._checkBounds(index);
 
   const pages = this._content.map(function (text, idx) {
-    return createPage(text, idx === index /* rendered */);
+    return createPage(text, idx >= index && idx <= lastRenderedPage);
   });
 
   this._container.innerHTML = '';

src/annotator/anchoring/test/pdf-test.js

@@ -134,6 +134,15 @@ describe('annotator.anchoring.pdf', function () {
         assert.equal(position.end, expectedPos + quote.length);
       });
     });
+
+    it('rejects when text selection spans multiple pages', () => {
+      viewer.setCurrentPage(2, 3);
+      const range = findText(container, 'occupied again? NODE A');
+
+      return pdfAnchoring.describe(container, range).catch(err => {
+        assert.equal(err.message, 'selecting across page breaks is not supported');
+      });
+    });
   });
 
   describe('#anchor', function () {