Issue #3321684: Should most validators that subscribe to PreCreate check readiness to update also subscribe to PreApply?

package_manager/tests/src/Kernel/PendingUpdatesValidatorTest.php

@@ -5,6 +5,7 @@ declare(strict_types = 1);
 namespace Drupal\Tests\package_manager\Kernel;
 
 use Drupal\package_manager\Event\PreCreateEvent;
+use Drupal\package_manager\Exception\StageValidationException;
 use Drupal\package_manager\ValidationResult;
 
 /**
@@ -64,4 +65,28 @@ class PendingUpdatesValidatorTest extends PackageManagerKernelTestBase {
     $this->assertResults([$result], PreCreateEvent::class);
   }
 
+  /**
+   * Tests that pending updates stop an operation from being applied.
+   */
+  public function testPendingUpdateAfterStaged(): void {
+    $this->registerPostUpdateFunctions();
+
+    $stage = $this->createStage();
+    $stage->create();
+    $stage->require(['drupal/core:9.8.1']);
+    // Make an additional post-update function available; the update registry
+    // will think it's pending.
+    require_once __DIR__ . '/../../fixtures/post_update.php';
+    $result = ValidationResult::createError([
+      'Some modules have database schema updates to install. You should run the <a href="/update.php">database update script</a> immediately.',
+    ]);
+    try {
+      $stage->apply();
+      $this->fail('Able to apply update even though there is pending update.');
+    }
+    catch (StageValidationException $exception) {
+      $this->assertValidationResultsEqual([$result], $exception->getResults());
+    }
+  }
+
 }