Issue #3150731 by andypost, Beakerboy, kim.pepper:...

Issue #3150731 by andypost, Beakerboy, kim.pepper: FileSystemModuleDiscoveryDataProviderTrait needs to use DIRECTORY_SEPARATOR

(cherry picked from commit a804607c4150265ad0e6e2fd2335011c3269c8ce)

core/tests/Drupal/KernelTests/FileSystemModuleDiscoveryDataProviderTrait.php

@@ -14,9 +14,10 @@ trait FileSystemModuleDiscoveryDataProviderTrait {
    *   An array of module names to test.
    */
   public function coreModuleListDataProvider() {
-    $module_dirs = array_keys(iterator_to_array(new \FilesystemIterator(__DIR__ . '/../../../modules/')));
-    $module_names = array_map(function ($path) {
-      return str_replace(__DIR__ . '/../../../modules/', '', $path);
+    $prefix = dirname(__DIR__, 3) . DIRECTORY_SEPARATOR . 'modules';
+    $module_dirs = array_keys(iterator_to_array(new \FilesystemIterator($prefix)));
+    $module_names = array_map(function ($path) use ($prefix) {
+      return str_replace($prefix . DIRECTORY_SEPARATOR, '', $path);
     }, $module_dirs);
     $modules_keyed = array_combine($module_names, $module_names);