Wait for the PDF to be loaded before doing anything

Closes #30531

app/assets/javascripts/blob/pdf/index.js

@@ -10,7 +10,7 @@ Vue.use(PDFLab, {
 export default () => {
   const el = document.getElementById('js-pdf-viewer');
 
-  new Vue({
+  return new Vue({
     el,
     data() {
       return {

spec/javascripts/blob/pdf/index_spec.js

@@ -3,6 +3,18 @@ import testPDF from './test.pdf';
 
 describe('PDF renderer', () => {
   let viewer;
+  let app;
+
+  const checkLoaded = (done) => {
+    if (app.loading) {
+      setTimeout(() => {
+        checkLoaded(done);
+      }, 100);
+    } else {
+      done();
+    }
+  };
+
   preloadFixtures('static/pdf_viewer.html.raw');
 
   beforeEach(() => {
@@ -21,11 +33,9 @@ describe('PDF renderer', () => {
 
   describe('successful response', () => {
     beforeEach((done) => {
-      renderPDF();
+      app = renderPDF();
 
-      setTimeout(() => {
-        done();
-      }, 500);
+      checkLoaded(done);
     });
 
     it('does not show loading icon', () => {
@@ -50,11 +60,9 @@ describe('PDF renderer', () => {
   describe('error getting file', () => {
     beforeEach((done) => {
       viewer.dataset.endpoint = 'invalid/endpoint';
-      renderPDF();
+      app = renderPDF();
 
-      setTimeout(() => {
-        done();
-      }, 500);
+      checkLoaded(done);
     });
 
     it('does not show loading icon', () => {