Optimize test ordering when directory is passed.

Closes #3450616

core/lib/Drupal/Core/Test/TestDiscovery.php

@@ -119,7 +119,9 @@ public function registerTestNamespaces() {
    * @param string $extension
    *   (optional) The name of an extension to limit discovery to; e.g., 'node'.
    * @param string[] $types
-   *   An array of included test types.
+   *   (optional) An array of included test types.
+   * @param string|null $directory
+   *   (optional) Limit discovered tests to a specific directory.
    *
    * @return array
    *   An array of tests keyed by the group name. If a test is annotated to
@@ -140,7 +142,7 @@ public function registerTestNamespaces() {
    * @todo Remove singular grouping; retain list of groups in 'group' key.
    * @see https://www.drupal.org/node/2296615
    */
-  public function getTestClasses($extension = NULL, array $types = []) {
+  public function getTestClasses($extension = NULL, array $types = [], ?string $directory = NULL) {
     if (!isset($extension) && empty($types)) {
       if (!empty($this->testClasses)) {
         return $this->testClasses;
@@ -148,7 +150,7 @@ public function getTestClasses($extension = NULL, array $types = []) {
     }
     $list = [];
 
-    $classmap = $this->findAllClassFiles($extension);
+    $classmap = $this->findAllClassFiles($extension, $directory);
 
     // Prevent expensive class loader lookups for each reflected test class by
     // registering the complete classmap of test classes to the class loader.
@@ -200,12 +202,14 @@ public function getTestClasses($extension = NULL, array $types = []) {
    *
    * @param string $extension
    *   (optional) The name of an extension to limit discovery to; e.g., 'node'.
+   * @param string|null $directory
+   *   (optional) Limit discovered tests to a specific directory.
    *
    * @return array
    *   A classmap containing all discovered class files; i.e., a map of
    *   fully-qualified classnames to path names.
    */
-  public function findAllClassFiles($extension = NULL) {
+  public function findAllClassFiles($extension = NULL, ?string $directory = NULL) {
     $classmap = [];
     $namespaces = $this->registerTestNamespaces();
     if (isset($extension)) {
@@ -215,7 +219,7 @@ public function findAllClassFiles($extension = NULL) {
     }
     foreach ($namespaces as $namespace => $paths) {
       foreach ($paths as $path) {
-        if (!is_dir($path)) {
+        if (!is_dir($path) || (!is_null($directory) && !str_contains($path, $directory))) {
           continue;
         }
         $classmap += static::scanDirectory($namespace, $path);