Issue #3279064: Consolidate logic around test stages

package_manager/tests/src/Kernel/PackageManagerKernelTestBase.php

@@ -31,6 +31,17 @@ abstract class PackageManagerKernelTestBase extends KernelTestBase {
     'package_manager_bypass',
   ];
 
+  /**
+   * The test staging root.
+   *
+   * This value must be set before create an test stage instance.
+   *
+   * @var string
+   *
+   * @see \Drupal\Tests\package_manager\Kernel\TestStageTrait::setStagingRoot()
+   */
+  public static $testStagingRoot;
+
   /**
    * The service IDs of any validators to disable.
    *
@@ -175,7 +186,7 @@ abstract class PackageManagerKernelTestBase extends KernelTestBase {
     // Create a staging root directory alongside the active directory.
     $stage_dir = vfsStream::newDirectory('stage');
     $this->vfsRoot->addChild($stage_dir);
-    TestStage::$stagingRoot = $stage_dir->url();
+    static::$testStagingRoot = $stage_dir->url();
 
     $path_locator = $this->mockPathLocator($active_dir->url());
 
@@ -254,7 +265,7 @@ trait TestStageTrait {
    */
   protected function setStagingRoot(): void {
     $mirror = new \ReflectionClass(Stage::class);
-    $this->tempStore->set($mirror->getConstant('TEMPSTORE_STAGING_ROOT_KEY'), TestStage::$stagingRoot);
+    $this->tempStore->set($mirror->getConstant('TEMPSTORE_STAGING_ROOT_KEY'), PackageManagerKernelTestBase::$testStagingRoot);
   }
 
   /**