Issue #3112432 by longwave, ridhimaabrol24, catch, alexpott: Prevent core,...

Issue #3112432 by longwave, ridhimaabrol24, catch, alexpott: Prevent core, stub simpletest module from being installed on new sites

core/modules/simpletest/simpletest.install

@@ -11,6 +11,25 @@
 use Drupal\Core\Test\TestDatabase;
 use Symfony\Component\Console\Output\NullOutput;
 
+/**
+ * Implements hook_requirements().
+ */
+function simpletest_requirements($phase) {
+  $requirements = [];
+  // Notify about the module being deprecated.
+  if ($phase == 'install' || $phase == 'runtime') {
+    $requirements['simpletest'] = [
+      'title' => t('SimpleTest'),
+      'severity' => REQUIREMENT_ERROR,
+      'description' => t('SimpleTest is has been removed from Drupal 9.0.0 and can no longer be installed. A contributed module is available for those who wish to continue using SimpleTest during the transition from Drupal 8 to 9. <a href=":change-record">See the change record for more information</a>.', [
+        ':change-record' => 'https://www.drupal.org/node/3091784',
+      ]),
+    ];
+  }
+
+  return $requirements;
+}
+
 /**
  * Implements hook_schema().
  */