be loud about failed learning track processing (github#25370)

* be loud about failed learning track processing

* rendering test

* undo whitespace cleanup

lib/process-learning-tracks.js

@@ -20,7 +20,9 @@ export default async function processLearningTracks(rawLearningTracks, context)
 
     // Find the data for the current product and track name.
     const track = context.site.data['learning-tracks'][context.currentProduct][renderedTrackName]
-    if (!track) continue
+    if (!track) {
+      throw new Error(`no learning track called '${renderedTrackName}'.`)
+    }
 
     // If there is no `versions` prop in the learning track frontmatter, assume the track should display in all versions.
     if (track.versions) {

tests/rendering/pages-with-learning-tracks.js

@@ -0,0 +1,28 @@
+import { jest, beforeAll, expect } from '@jest/globals'
+
+import { getDOM } from '../helpers/supertest.js'
+import { loadPages } from '../../lib/page-data.js'
+
+describe('process learning tracks', () => {
+  let pageList
+
+  // Because calling `loadPages` will trigger a warmup, this can potentially
+  // be very slow in CI. So we need a timeout.
+  jest.setTimeout(60 * 1000)
+
+  beforeAll(async () => {
+    // Only doing English because they're the only files we do PRs for.
+    pageList = (await loadPages()).filter((page) => page.languageCode === 'en')
+  })
+
+  test('pages with learningTracks ', async () => {
+    for (const page of pageList) {
+      if (page.learningTracks && page.learningTracks.length > 0) {
+        for (const permalink of page.permalinks) {
+          const $ = await getDOM(permalink.href)
+          expect($('[data-testid="learning-track"]').length).toBeGreaterThanOrEqual(1)
+        }
+      }
+    }
+  })
+})