test: check replaced iff translatable comment

All translatable comments should be replaced, but nothing else.

curriculum/test/utils/plugins/get-html-comments.js

@@ -0,0 +1,20 @@
+const { isEmpty } = require('lodash');
+const visit = require('unist-util-visit');
+const { commentToData } = require('../comment-to-data');
+
+function plugin() {
+  return transformer;
+
+  function transformer(tree, file) {
+    if (isEmpty(file.data)) {
+      file.data = {};
+    }
+    visit(tree, 'comment', visitor);
+
+    function visitor(node) {
+      commentToData(file, node.value.trim());
+    }
+  }
+}
+
+module.exports = plugin;