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

tests/src/Build/TemplateProjectSiteTestBase.php

+<?php
+
+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.
+   *
+   * @return \Composer\Json\JsonFile
+   *   A wrapper around the repository file.
+   */
+  protected function createVendorRepository(): JsonFile {
+    $file = new JsonFile($this->getWorkspaceDirectory() . '/vendor_packages.json');
+
+    // Build out package definitions for everything installed in the vendor
+    // directory.
+    $packages = [];
+    foreach ($this->getPackagesFromLockFile() as $package) {
+      $name = $package['name'];
+      $path = $this->getDrupalRoot() . "/vendor/$name";
+      // We are building a set of path repositories to projects in the vendor
+      // directory, so we will skip any project that does not exist in vendor.
+      // Also skip the projects that are symlinked in vendor. These are in our
+      // metapackage. They will be represented as path repositories in the test
+      // project's composer.json.
+      if (is_dir($path) && !is_link($path)) {
+        $version = $package['version'];
+        unset($package['source']);
+        $package['dist'] = [
+          'type' => 'path',
+          'url' => $path,
+        ];
+        $packages[$name][$version] = $package;
+      }
+    }
+    $file->write(['packages' => $packages]);
+    return $file;
+  }
+
+  /**
+   * Reads all package information from the composer.lock file.
+   *
+   * @return mixed[][]
+   *   All package information (including dev packages) from the lock file.
+   */
+  private function getPackagesFromLockFile(): array {
+    $data = file_get_contents($this->getDrupalRoot() . '/composer.lock');
+    $data = JsonFile::parseJson($data);
+
+    return array_merge($data['packages'], $data['packages-dev']);
+  }
+
+}