Issue #3328234: Improve test DX *and* confidence: assert VFS state

package_manager/tests/src/Kernel/PackageManagerKernelTestBase.php

@@ -255,11 +255,22 @@ abstract class PackageManagerKernelTestBase extends KernelTestBase {
     // Create the active directory and copy its contents from a fixture.
     $active_dir = $root . DIRECTORY_SEPARATOR . 'active';
     $this->assertTrue(mkdir($active_dir));
+    if ($this->useVfs) {
+      // Move vfs://root/sites to vfs://root/active/sites.
+      $sites_in_vfs = vfsStream::url('root/sites');
+      rename($sites_in_vfs, $sites_in_vfs . '/active');
+    }
     static::copyFixtureFilesTo($source_dir, $active_dir);
 
     // Override siteDirectory to point to root/active/... instead of root/... .
-    $test_site_path = str_replace('vfs://root/', '', $this->siteDirectory);
-    $this->siteDirectory = vfsStream::url('root/active/' . $test_site_path);
+    if ($this->useVfs) {
+      $test_site_path = str_replace('vfs://root/', '', $this->siteDirectory);
+      $this->siteDirectory = vfsStream::url('root/active/' . $test_site_path);
+    }
+    else {
+      $test_site_path = str_replace('vfs://root/', '', $this->siteDirectory);
+      $this->siteDirectory = $active_dir . $test_site_path;
+    }
     // Override KernelTestBase::setUpFilesystem's Settings object.
     $settings = Settings::getInstance() ? Settings::getAll() : [];
     $settings['file_public_path'] = $this->siteDirectory . '/files';