Menu tree caching is broken

I thought that's why we do unit tests? :)

This is emberassing tbh.
This still obviously does not cover all of the menu tree building but at least a little bit more.

2: menu_tree-2229283-2.patch queued for re-testing.

Rerolled.

Maybe this is it.

8: menu_tree-2229283-8.patch queued for re-testing.

Updating the patch. Please review.

Thank you

+++ b/core/modules/menu_link/tests/Drupal/menu_link/Tests/MenuTreeTest.php
@@ -321,6 +328,78 @@ public function testGetActiveTrailIdsWithoutPreferredLink() {
+    $this->menuTree->buildTree('test_menu');
+    $this->menuTree->buildTree('test_menu');

Is that intentional..? If so, it could use a comment as to why we do that.

// Ensure that the static caching triggered.

$this->cacheBackend->expects($this->exactly(1))
  ->method('get');

$this->menuTree->buildTree('test_menu');
$this->menuTree->buildTree('test_menu');