Issue #3258056: Simplify Stage::dispatch exception handling

tests/src/Functional/UpdaterFormTest.php

@@ -3,6 +3,7 @@
 namespace Drupal\Tests\automatic_updates\Functional;
 
 use Drupal\automatic_updates\Event\ReadinessCheckEvent;
+use Drupal\automatic_updates\Exception\UpdateException;
 use Drupal\package_manager\Event\PreCreateEvent;
 use Drupal\package_manager\ValidationResult;
 use Drupal\automatic_updates_test\ReadinessChecker\TestChecker1;
@@ -175,9 +176,9 @@ class UpdaterFormTest extends AutomaticUpdatesFunctionalTestBase {
     $assert_session->pageTextNotContains((string) $message);
     TestChecker1::setTestResult(NULL, ReadinessCheckEvent::class);
 
-    // Set an exception that the validator will throw, so we can test what
+    // Repackage the validation error as an exception, so we can test what
     // happens if a validator throws once the update has started.
-    $error = new \RuntimeException('The update exploded.');
+    $error = new UpdateException($expected_results, 'The update exploded.');
     TestChecker1::setException($error, PreCreateEvent::class);
     $session->reload();
     $assert_session->pageTextNotContains(static::$errorsExplanation);
@@ -190,7 +191,10 @@ class UpdaterFormTest extends AutomaticUpdatesFunctionalTestBase {
     $this->assertUpdateStagedTimes(0);
     $assert_session->pageTextContainsOnce('An error has occurred.');
     $page->clickLink('the error page');
-    // We should see the exception message.
+    $assert_session->pageTextContainsOnce((string) $expected_results[0]->getMessages()[0]);
+    // Since there's only one error message, we shouldn't see the summary...
+    $assert_session->pageTextNotContains($expected_results[0]->getSummary());
+    // ...but we should see the exception message.
     $assert_session->pageTextContainsOnce('The update exploded.');
     // If the error is thrown in PreCreateEvent the update stage will not have
     // been created.