diff --git a/DEVELOPING.md b/DEVELOPING.md
index db33925d7e4694a1b9d45c2380caa7eaabb8ee57..7ff408abc1445e7840f5ac42092908dc8b815c98 100644
--- a/DEVELOPING.md
+++ b/DEVELOPING.md
@@ -11,7 +11,6 @@ For development and running the module's tests, Automatic Updates assumes you ar
 ```
 git clone https://git.drupalcode.org/project/drupal.git --branch 9.5.x auto-updates-dev
 cd auto-updates-dev
-composer config platform.php 7.4.0
 composer install
 ```
 Replace `9.5.x` with the desired development branch of Drupal core. Be sure to point your web server to the `auto-updates-dev` directory, so you can access this code base in a browser.
@@ -25,7 +24,7 @@ git clone --branch '8.x-2.x' https://git.drupalcode.org/project/automatic_update
 ### Step 3: Install dependencies
 From the Drupal repository root:
 ```
-composer require php-tuf/composer-stager "symfony/config:^4.4 || ^6.1"
+composer require php-tuf/composer-stager "symfony/config:^4.4 || ^6.1" --ignore-platform-req php
 git reset --hard
 ```
 Note: If you switch to a different branch of Drupal core and delete the `vendor` directory, you will need to do this step again after running `composer install`.
diff --git a/package_manager/tests/src/Build/TemplateProjectTestBase.php b/package_manager/tests/src/Build/TemplateProjectTestBase.php
index f1ff8bd0c190760147365ee5cdb9d4f329ef2867..ed711eabffcb5d45d8230f598cfb6a301452c15b 100644
--- a/package_manager/tests/src/Build/TemplateProjectTestBase.php
+++ b/package_manager/tests/src/Build/TemplateProjectTestBase.php
@@ -237,7 +237,7 @@ END;
     $packages = [];
     $drupal_root = $this->getDrupalRoot();
 
-    foreach ($this->getPackagesFromLockFile() as $package) {
+    foreach ($this->getInstalledPackages() as $package) {
       $name = $package['name'];
       $path = "$drupal_root/vendor/$name";
 
@@ -273,23 +273,19 @@ END;
   }
 
   /**
-   * Returns all package information from the lock file.
+   * Returns all package information from the `installed.json` file.
    *
    * @return mixed[][]
-   *   All package data from the lock file.
+   *   All package data from the `installed.json` file.
    */
-  private function getPackagesFromLockFile(): array {
-    $lock = $this->getDrupalRoot() . '/composer.lock';
-    $this->assertFileExists($lock);
+  private function getInstalledPackages(): array {
+    $installed = $this->getDrupalRoot() . '/vendor/composer/installed.json';
+    $this->assertFileExists($installed);
 
-    $lock = file_get_contents($lock);
-    $lock = json_decode($lock, TRUE, JSON_THROW_ON_ERROR);
+    $installed = file_get_contents($installed);
+    $installed = json_decode($installed, TRUE, JSON_THROW_ON_ERROR);
 
-    $lock += [
-      'packages' => [],
-      'packages-dev' => [],
-    ];
-    return array_merge($lock['packages'], $lock['packages-dev']);
+    return $installed['packages'];
   }
 
   /**