test: check replaced iff translatable comment

All translatable comments should be replaced, but nothing else.

curriculum/test/utils/extract-js-comments.js

@@ -0,0 +1,17 @@
+const acorn = require('acorn');
+const { commentToData } = require('./comment-to-data');
+
+const parser = acorn.Parser;
+
+function extractComments(js) {
+  let comments = [];
+  const file = { data: {} };
+  parser.parse(js, { onComment: comments, ecmaVersion: 2020 });
+
+  comments
+    .map(({ value }) => value.trim())
+    .forEach(comment => commentToData(file, comment));
+  return file.data;
+}
+
+module.exports = extractComments;