Improve UpdatePathTestBase debuggablity

Problem/Motivation

When any update path test fails we just check for TRUE/FALSE whether we need some additional updates. This doesn't help people to figure out for example which updates didn't got executed in the test.

Proposed resolution

Do something along

+++ b/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
@@ -265,7 +265,15 @@ protected function runUpdates() {
-    $this->assertFalse(\Drupal::service('entity.definition_update_manager')->needsUpdates(), 'After all updates ran, entity schema is up to date.');
+    $needs_updates = \Drupal::entityDefinitionUpdateManager()->needsUpdates();
+    $this->assertFalse($needs_updates, 'After all updates ran, entity schema is up to date.');
+    if ($needs_updates) {
+      foreach (\Drupal::entityDefinitionUpdateManager()->getChangeSummary() as $entity_type_id => $summary) {
+        foreach ($summary as $message) {
+          $this->fail($message);
+        }
+      }
+    }

Remaining tasks

User interface changes

API changes

Data model changes