Issue #3254166: Build tests should not modify dependencies' composer.json files

tests/src/Build/TemplateProjectSiteTestBase.php

@@ -4,12 +4,42 @@ namespace Drupal\Tests\automatic_updates\Build;
 
 use Composer\Json\JsonFile;
 use Drupal\BuildTests\QuickStart\QuickStartTestBase;
+use Drupal\Composer\Composer;
 
 /**
  * Base class for tests which build a test site from a template project.
  */
 abstract class TemplateProjectSiteTestBase extends QuickStartTestBase {
 
+  /**
+   * Returns path repository definitions for core's Composer packages.
+   *
+   * @param string $group
+   *   The package group. Can be one of 'Template', 'Metapackage', or 'Plugin'.
+   *
+   * @return array[]
+   *   A set of path repository definitions, keyed by package name.
+   */
+  protected function getPathRepositories(string $group): array {
+    /** @var \SplFileInfo[] $files */
+    $files = Composer::composerSubprojectPaths($this->getDrupalRoot(), $group);
+
+    $repositories = [];
+    foreach ($files as $file) {
+      $json = new JsonFile($file->getPathname());
+      $data = $json->read();
+      $name = $data['name'];
+      $repositories[$name] = [
+        'type' => 'path',
+        'url' => $file->getPath(),
+        'options' => [
+          'symlink' => FALSE,
+        ],
+      ];
+    }
+    return $repositories;
+  }
+
   /**
    * Creates a Composer repository of all packages installed in vendor.
    *