Fix intermittent failure in the "supports specifying a custom origin" viewer integration test

The problem in the original code is that `getTextAt` is called too
early and therefore returns unexpected text content. This can happen
because we call `increaseScale` and then wait for the page's text layer
to be visible, but it can take some time before the zoom actually
occurs/completes in the viewer and in the meantime the old (pre-zoom)
text layer may still be visible, causing us to continue too soon because
we don't validate that we're dealing with the post-zoom text layer.

This commit fixes the issue by simply waiting for the expected text to
show up at the given origin coordinates, which makes the test work
independent of viewer actions/timing.

Author: timvandermeij

test/integration/viewer_spec.mjs

@@ -42,23 +42,40 @@ describe("PDF viewer", () => {
       await closePages(pages);
     });
 
-    async function getTextAt(page, pageNumber, coordX, coordY) {
-      await page.waitForFunction(
-        pageNum =>
-          !document.querySelector(
-            `.page[data-page-number="${pageNum}"] > .textLayer`
-          ).hidden,
-        {},
-        pageNumber
+    async function waitForTextAfterZoom(page, originX, originY, scale, text) {
+      const handlePromise = await createPromise(page, resolve => {
+        const callback = e => {
+          if (e.pageNumber === 2) {
+            window.PDFViewerApplication.eventBus.off(
+              "textlayerrendered",
+              callback
+            );
+            resolve();
+          }
+        };
+        window.PDFViewerApplication.eventBus.on("textlayerrendered", callback);
+      });
+
+      await page.evaluate(
+        (scaleFactor, origin) => {
+          window.PDFViewerApplication.pdfViewer.updateScale({
+            drawingDelay: 0,
+            scaleFactor,
+            origin,
+          });
+        },
+        scale,
+        [originX, originY]
       );
-      return page.evaluate(
-        (x, y) => document.elementFromPoint(x, y)?.textContent,
-        coordX,
-        coordY
+
+      await awaitPromise(handlePromise);
+
+      await page.waitForFunction(
+        `document.elementFromPoint(${originX}, ${originY})?.textContent === "${text}"`
       );
     }
 
-    it("supports specifiying a custom origin", async () => {
+    it("supports specifying a custom origin", async () => {
       await Promise.all(
         pages.map(async ([browserName, page]) => {
           // We use this text span of page 2 because:
@@ -72,33 +89,8 @@ describe("PDF viewer", () => {
           const originX = rect.x + rect.width / 2;
           const originY = rect.y + rect.height / 2;
 
-          await page.evaluate(
-            origin => {
-              window.PDFViewerApplication.pdfViewer.increaseScale({
-                scaleFactor: 2,
-                origin,
-              });
-            },
-            [originX, originY]
-          );
-          const textAfterZoomIn = await getTextAt(page, 2, originX, originY);
-          expect(textAfterZoomIn)
-            .withContext(`In ${browserName}, zoom in`)
-            .toBe(text);
-
-          await page.evaluate(
-            origin => {
-              window.PDFViewerApplication.pdfViewer.decreaseScale({
-                scaleFactor: 0.8,
-                origin,
-              });
-            },
-            [originX, originY]
-          );
-          const textAfterZoomOut = await getTextAt(page, 2, originX, originY);
-          expect(textAfterZoomOut)
-            .withContext(`In ${browserName}, zoom out`)
-            .toBe(text);
+          await waitForTextAfterZoom(page, originX, originY, 2, text);
+          await waitForTextAfterZoom(page, originX, originY, 0.8, text);
         })
       );
     });