interdiff impossible; taking evasive action
reverted:
--- b/core/modules/system/tests/src/Kernel/Module/InstallTest.php
+++ a/core/modules/system/tests/src/Functional/Module/InstallTest.php
@@ -1,64 +1,44 @@
 <?php
 
+namespace Drupal\Tests\system\Functional\Module;
-namespace Drupal\Tests\system\Kernel\Module;
 
+use Drupal\Core\Database\Database;
 use Drupal\Core\Extension\ExtensionNameLengthException;
+use Drupal\Tests\BrowserTestBase;
-use Drupal\KernelTests\KernelTestBase;
 
 /**
  * Tests the installation of modules.
  *
  * @group Module
  */
+class InstallTest extends BrowserTestBase {
-class InstallTest extends KernelTestBase {
 
   /**
+   * Modules to enable.
-   * The module installer service.
    *
+   * @var array
-   * @var \Drupal\Core\Extension\ModuleInstallerInterface
    */
+  public static $modules = ['module_test'];
-  protected $moduleInstaller;
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-
-    $this->moduleInstaller = $this->container->get('module_installer');
-    $this->moduleInstaller->install([
-      'module_test',
-      'system',
-      'user',
-    ]);
-  }
 
   /**
    * Verify that drupal_get_schema() can be used during module installation.
    */
   public function testGetSchemaAtInstallTime() {
+    // @see module_test_install()
+    $value = Database::getConnection()->query("SELECT data FROM {module_test}")->fetchField();
+    $this->assertIdentical($value, 'varchar');
-    $database = $this->container->get('database');
-    $value = $database->select('module_test')
-      ->fields('module_test', ['data'])
-      ->execute()
-      ->fetchField();
-    $this->assertEquals('varchar', $value);
   }
 
   /**
    * Tests enabling User module once more.
    *
    * Regression: The installer might enable a module twice due to automatic
+   * dependency resolution. A bug caused the stored weight for User module to
-   * dependency resolution. A bug caused the stored weight for user.module to
    * be an array.
    */
   public function testEnableUserTwice() {
+    \Drupal::service('module_installer')->install(['user'], FALSE);
+    $this->assertIdentical($this->config('core.extension')->get('module.user'), 0);
-    $this->moduleInstaller->install(['user'], FALSE);
-    $this->assertSame(0, $this->config('core.extension')->get('module.user'));
-
-    // To avoid false positives, ensure that a module that does not exist does
-    // not return exactly zero.
-    $this->assertNotSame(0, $this->config('core.extension')->get('module.does_not_exist'));
   }
 
   /**
@@ -66,32 +46,24 @@
    */
   public function testRequiredModuleSchemaVersions() {
     $version = drupal_get_installed_schema_version('system', TRUE);
+    $this->assertTrue($version > 0, 'System module version is > 0.');
-    $this->assertGreaterThan(0, $version);
     $version = drupal_get_installed_schema_version('user', TRUE);
+    $this->assertTrue($version > 0, 'User module version is > 0.');
-    $this->assertGreaterThan(0, $version);
 
+    $post_update_key_value = \Drupal::keyValue('post_update');
-    $post_update_key_value = $this->container->get('keyvalue')->get('post_update');
     $existing_updates = $post_update_key_value->get('existing_updates', []);
+    $this->assertTrue(in_array('module_test_post_update_test', $existing_updates));
-
-    $this->assertContains('module_test_post_update_test', $existing_updates);
   }
 
   /**
    * Ensures that post update functions are removed on uninstall.
    */
   public function testUninstallPostUpdateFunctions() {
+    \Drupal::service('module_installer')->uninstall(['module_test']);
-    // First, to avoid false positives, ensure that the post_update function
-    // exists while the module is still installed.
-    $post_update_key_value = $this->container->get('keyvalue')->get('post_update');
-    $existing_updates = $post_update_key_value->get('existing_updates', []);
-    $this->assertContains('module_test_post_update_test', $existing_updates);
-
-    // Uninstall the module.
-    $this->moduleInstaller->uninstall(['module_test']);
 
+    $post_update_key_value = \Drupal::keyValue('post_update');
-    // Ensure the post update function is no longer listed.
     $existing_updates = $post_update_key_value->get('existing_updates', []);
+    $this->assertFalse(in_array('module_test_post_update_test', $existing_updates));
-    $this->assertNotContains('module_test_post_update_test', $existing_updates);
   }
 
   /**
@@ -99,18 +71,24 @@
    */
   public function testModuleNameLength() {
     $module_name = 'invalid_module_name_over_the_maximum_allowed_character_length';
+    $message = format_string('Exception thrown when enabling module %name with a name length over the allowed maximum', ['%name' => $module_name]);
+    try {
+      $this->container->get('module_installer')->install([$module_name]);
+      $this->fail($message);
+    }
+    catch (ExtensionNameLengthException $e) {
+      $this->pass($message);
+    }
-    $this->setExpectedException(ExtensionNameLengthException::class);
-    $this->moduleInstaller->install([$module_name]);
-  }
 
-  /**
-   * Tests that an exception is thrown when a module name is too long.
-   */
-  public function testModuleNameLengthWithDependencyCheck() {
     // Since for the UI, the submit callback uses FALSE, test that too.
+    $message = format_string('Exception thrown when enabling as if via the UI the module %name with a name length over the allowed maximum', ['%name' => $module_name]);
+    try {
+      $this->container->get('module_installer')->install([$module_name], FALSE);
+      $this->fail($message);
+    }
+    catch (ExtensionNameLengthException $e) {
+      $this->pass($message);
+    }
-    $module_name = 'invalid_module_name_over_the_maximum_allowed_character_length';
-    $this->setExpectedException(ExtensionNameLengthException::class);
-    $this->moduleInstaller->install([$module_name], FALSE);
   }
 
 }
unchanged:
--- /dev/null
+++ b/core/modules/system/tests/src/Kernel/Module/InstallTest.php
@@ -0,0 +1,123 @@
+<?php
+
+namespace Drupal\Tests\system\Kernel\Module;
+
+use Drupal\Core\Extension\ExtensionNameLengthException;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests the installation of modules.
+ *
+ * @group Module
+ */
+class InstallTest extends KernelTestBase {
+
+  /**
+   * The module installer service.
+   *
+   * @var \Drupal\Core\Extension\ModuleInstallerInterface
+   */
+  protected $moduleInstaller;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->moduleInstaller = $this->container->get('module_installer');
+    $this->moduleInstaller->install([
+      'module_test',
+      'system',
+      'user',
+    ]);
+  }
+
+  /**
+   * Verify that drupal_get_schema() can be used during module installation.
+   */
+  public function testGetSchemaAtInstallTime(): void {
+    // @see module_test_install()
+    $database = $this->container->get('database');
+    $value = $database->select('module_test')
+      ->fields('module_test', ['data'])
+      ->execute()
+      ->fetchField();
+    $this->assertEquals('varchar', $value);
+  }
+
+  /**
+   * Tests enabling User module once more.
+   *
+   * Regression: The installer might enable a module twice due to automatic
+   * dependency resolution. A bug caused the stored weight for user.module to
+   * be an array.
+   */
+  public function testEnableUserTwice(): void {
+    $this->moduleInstaller->install(['user'], FALSE);
+    $this->assertSame(0, $this->config('core.extension')->get('module.user'));
+
+    // To avoid false positives, ensure that a module that does not exist does
+    // not return exactly zero.
+    $this->assertNotSame(0, $this->config('core.extension')
+      ->get('module.does_not_exist'));
+  }
+
+  /**
+   * Tests recorded schema versions of early installed modules in the installer.
+   */
+  public function testRequiredModuleSchemaVersions(): void {
+    /** @var \Drupal\Core\Update\UpdateHookRegistry $update_registry */
+    $update_registry = \Drupal::service('update.update_hook_registry');
+    $version = $update_registry->getInstalledVersion('system');
+    $this->assertGreaterThan(0, $version);
+    $version = $update_registry->getInstalledVersion('user');
+    $this->assertGreaterThan(0, $version);
+
+    $post_update_key_value = \Drupal::keyValue('post_update');
+    $existing_updates = $post_update_key_value->get('existing_updates', []);
+    $this->assertContains('module_test_post_update_test', $existing_updates);
+  }
+
+  /**
+   * Ensures that post update functions are removed on uninstallation.
+   */
+  public function testUninstallPostUpdateFunctions(): void {
+    // First, to avoid false positives, ensure that the post_update function
+    // exists while the module is still installed.
+    $post_update_key_value = $this->container->get('keyvalue')
+      ->get('post_update');
+    $existing_updates = $post_update_key_value->get('existing_updates', []);
+    $this->assertContains('module_test_post_update_test', $existing_updates);
+
+    // Uninstall the module.
+    $this->moduleInstaller->uninstall(['module_test']);
+
+    // Ensure the post update function is no longer listed.
+    $existing_updates = $post_update_key_value->get('existing_updates', []);
+    $this->assertNotContains('module_test_post_update_test', $existing_updates);
+  }
+
+  /**
+   * Tests that an exception is thrown when a module name is too long.
+   */
+  public function testModuleNameLength(): void {
+    $module_name = 'invalid_module_name_over_the_maximum_allowed_character_length';
+    $this->expectException(ExtensionNameLengthException::class);
+    $this->expectExceptionMessage("Module name 'invalid_module_name_over_the_maximum_allowed_character_length' is over the maximum allowed length of 50 characters");
+    $this->moduleInstaller->install([$module_name]);
+  }
+
+  /**
+   * Tests that an exception is thrown when a module name is too long.
+   *
+   * We do this without checking dependencies for the module to install.
+   */
+  public function testModuleNameLengthWithoutDependencyCheck(): void {
+    $module_name = 'invalid_module_name_over_the_maximum_allowed_character_length';
+    $this->expectException(ExtensionNameLengthException::class);
+    $this->expectExceptionMessage("Module name 'invalid_module_name_over_the_maximum_allowed_character_length' is over the maximum allowed length of 50 characters");
+    $this->moduleInstaller->install([$module_name], FALSE);
+  }
+
+}
only in patch2:
unchanged:
--- a/core/modules/system/tests/src/Functional/Module/InstallTest.php
+++ /dev/null
@@ -1,102 +0,0 @@
-<?php
-
-namespace Drupal\Tests\system\Functional\Module;
-
-use Drupal\Component\Render\FormattableMarkup;
-use Drupal\Core\Database\Database;
-use Drupal\Core\Extension\ExtensionNameLengthException;
-use Drupal\Tests\BrowserTestBase;
-
-/**
- * Tests the installation of modules.
- *
- * @group Module
- */
-class InstallTest extends BrowserTestBase {
-
-  /**
-   * Modules to enable.
-   *
-   * @var array
-   */
-  protected static $modules = ['module_test'];
-
-  /**
-   * {@inheritdoc}
-   */
-  protected $defaultTheme = 'stark';
-
-  /**
-   * Verify that drupal_get_schema() can be used during module installation.
-   */
-  public function testGetSchemaAtInstallTime() {
-    // @see module_test_install()
-    $value = Database::getConnection()->select('module_test', 'mt')->fields('mt', ['data'])->execute()->fetchField();
-    $this->assertSame('varchar', $value);
-  }
-
-  /**
-   * Tests enabling User module once more.
-   *
-   * Regression: The installer might enable a module twice due to automatic
-   * dependency resolution. A bug caused the stored weight for User module to
-   * be an array.
-   */
-  public function testEnableUserTwice() {
-    \Drupal::service('module_installer')->install(['user'], FALSE);
-    $this->assertSame(0, $this->config('core.extension')->get('module.user'));
-  }
-
-  /**
-   * Tests recorded schema versions of early installed modules in the installer.
-   */
-  public function testRequiredModuleSchemaVersions() {
-    /** @var \Drupal\Core\Update\UpdateHookRegistry $update_registry */
-    $update_registry = \Drupal::service('update.update_hook_registry');
-    $version = $update_registry->getInstalledVersion('system');
-    $this->assertGreaterThan(0, $version);
-    $version = $update_registry->getInstalledVersion('user');
-    $this->assertGreaterThan(0, $version);
-
-    $post_update_key_value = \Drupal::keyValue('post_update');
-    $existing_updates = $post_update_key_value->get('existing_updates', []);
-    $this->assertContains('module_test_post_update_test', $existing_updates);
-  }
-
-  /**
-   * Ensures that post update functions are removed on uninstall.
-   */
-  public function testUninstallPostUpdateFunctions() {
-    \Drupal::service('module_installer')->uninstall(['module_test']);
-
-    $post_update_key_value = \Drupal::keyValue('post_update');
-    $existing_updates = $post_update_key_value->get('existing_updates', []);
-    $this->assertNotContains('module_test_post_update_test', $existing_updates);
-  }
-
-  /**
-   * Tests that an exception is thrown when a module name is too long.
-   */
-  public function testModuleNameLength() {
-    $module_name = 'invalid_module_name_over_the_maximum_allowed_character_length';
-    $message = new FormattableMarkup('Exception thrown when enabling module %name with a name length over the allowed maximum', ['%name' => $module_name]);
-    try {
-      $this->container->get('module_installer')->install([$module_name]);
-      $this->fail($message);
-    }
-    catch (\Exception $e) {
-      $this->assertInstanceOf(ExtensionNameLengthException::class, $e);
-    }
-
-    // Since for the UI, the submit callback uses FALSE, test that too.
-    $message = new FormattableMarkup('Exception thrown when enabling as if via the UI the module %name with a name length over the allowed maximum', ['%name' => $module_name]);
-    try {
-      $this->container->get('module_installer')->install([$module_name], FALSE);
-      $this->fail($message);
-    }
-    catch (\Exception $e) {
-      $this->assertInstanceOf(ExtensionNameLengthException::class, $e);
-    }
-  }
-
-}