diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5c7619a..613941c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,10 +4,17 @@ Changelog
 5.x
 ===
 
+5.0.1
+-----
+
+* Cleanup PHP 8.1 language features.
+* Simplify configuration code.
+
 5.0.0
 -----
 
 * Drop support for Symfony < 6.4
+* Drop support for PHP < 8.1
 * The default framework configuration no longer enables validation attributes.
 * The PHPCR-ODM additional namespace is expected to use attributes rather than annotations.
 
diff --git a/composer.json b/composer.json
index 12d8681..07dd10e 100644
--- a/composer.json
+++ b/composer.json
@@ -14,8 +14,11 @@
         "symfony/browser-kit": "^6.4 || ^7.0"
     },
     "require-dev": {
+        "ext-dom": "*",
         "doctrine/doctrine-bundle": "^1.8 || ^2.0",
+        "doctrine/phpcr-odm": "^2.0",
         "doctrine/phpcr-bundle": "^3.0",
+        "jackalope/jackalope-doctrine-dbal": "^2.0",
         "symfony/console": "^6.4 || ^7.0",
         "symfony/dependency-injection": "^6.4 || ^7.0",
         "symfony/doctrine-bridge": "^6.4 || ^7.0",
diff --git a/src/DependencyInjection/Compiler/TestContainerPass.php b/src/DependencyInjection/Compiler/TestContainerPass.php
index 5df4773..4514164 100644
--- a/src/DependencyInjection/Compiler/TestContainerPass.php
+++ b/src/DependencyInjection/Compiler/TestContainerPass.php
@@ -20,18 +20,16 @@
 class TestContainerPass implements CompilerPassInterface
 {
     /**
-     * An array of service id's which should be public in a test scenario.
-     *
-     * @var array
+     * @var string[] Service id's which should be public in a test scenario
      */
-    private $services = [];
+    private array $services;
 
     public function __construct(array $services = [])
     {
         $this->services = $services;
     }
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         foreach ($container->getDefinitions() as $id => $definition) {
             if (\in_array($id, $this->services, true)) {
diff --git a/src/Functional/BaseTestCase.php b/src/Functional/BaseTestCase.php
index 022559e..3a77b68 100644
--- a/src/Functional/BaseTestCase.php
+++ b/src/Functional/BaseTestCase.php
@@ -113,15 +113,12 @@ protected function getFrameworkBundleClient(): KernelBrowser
      *
      * @see self::getDbManager
      */
-    protected function db($type)
+    protected function db(string $type): PhpcrDecorator|PHPCR|ORM
     {
         return $this->getDbManager($type);
     }
 
-    /**
-     * @return ORM|PHPCR
-     */
-    protected function getDbManager(string $type)
+    protected function getDbManager(string $type): PhpcrDecorator|PHPCR|ORM
     {
         if (isset($this->dbManagers[$type])) {
             return $this->dbManagers[$type];
diff --git a/src/Functional/DbManager/PHPCR.php b/src/Functional/DbManager/PHPCR.php
index 6f34cbb..f25b931 100644
--- a/src/Functional/DbManager/PHPCR.php
+++ b/src/Functional/DbManager/PHPCR.php
@@ -23,7 +23,7 @@
 
 class PHPCR
 {
-    protected $container;
+    protected ContainerInterface $container;
 
     protected ?DocumentManager $om = null;
 
diff --git a/src/HttpKernel/TestKernel.php b/src/HttpKernel/TestKernel.php
index 8092d5b..bfc3343 100644
--- a/src/HttpKernel/TestKernel.php
+++ b/src/HttpKernel/TestKernel.php
@@ -32,9 +32,9 @@
  */
 abstract class TestKernel extends Kernel
 {
-    protected $bundleSets = [];
+    protected array $bundleSets = [];
 
-    protected $requiredBundles = [];
+    protected array $requiredBundles = [];
 
     /**
      * Register commonly needed bundle sets and then
@@ -42,7 +42,7 @@ abstract class TestKernel extends Kernel
      * concrete kernel configure itself using the abstracvt
      * configure() command.
      */
-    public function __construct($env, $debug)
+    public function __construct(string $env, bool $debug)
     {
         $defaultBundles = [
             FrameworkBundle::class,
@@ -72,7 +72,7 @@ public function __construct($env, $debug)
      *    $this->addBundle(new MyBundle);
      *    $this->addBundles(array(new Bundle1, new Bundle2));
      */
-    abstract protected function configure();
+    abstract protected function configure(): void;
 
     /**
      * Register a set of bundles with the given name.
@@ -80,15 +80,17 @@ abstract protected function configure();
      * This method does not add the bundles to the kernel,
      * it just makes a set available.
      */
-    public function registerBundleSet($name, $bundles)
+    public function registerBundleSet(string $name, array $bundles): void
     {
         $this->bundleSets[$name] = $bundles;
     }
 
     /**
      * The bundles in the named sets will be added to the Kernel.
+     *
+     * @param string[] $names
      */
-    public function requireBundleSets(array $names)
+    public function requireBundleSets(array $names): void
     {
         foreach ($names as $name) {
             $this->requireBundleSet($name);
@@ -102,7 +104,7 @@ public function requireBundleSets(array $names)
      * This enables us to declare pre-defined bundle sets without
      * worrying if the bundle is actually present or not.
      */
-    public function requireBundleSet($name)
+    public function requireBundleSet(string $name): void
     {
         if (!isset($this->bundleSets[$name])) {
             throw new \InvalidArgumentException(sprintf(
@@ -127,7 +129,7 @@ public function requireBundleSet($name)
     /**
      * Add concrete bundles to the kernel.
      */
-    public function addBundles(array $bundles)
+    public function addBundles(array $bundles): void
     {
         foreach ($bundles as $bundle) {
             $this->addBundle($bundle);
@@ -137,7 +139,7 @@ public function addBundles(array $bundles)
     /**
      * Add a concrete bundle to the kernel.
      */
-    public function addBundle(BundleInterface $bundle)
+    public function addBundle(BundleInterface $bundle): void
     {
         $this->requiredBundles[] = $bundle;
     }
@@ -153,28 +155,22 @@ public function registerBundles(): iterable
     }
 
     /**
-     * Returns the KernelDir of the CHILD class,
+     * Returns the project directory of the CHILD class,
      * i.e. the concrete implementation in the bundles
      * src/ directory (or wherever).
      */
-    public function getKernelDir()
-    {
-        return $this->getProjectDir();
-    }
-
     public function getProjectDir(): string
     {
         $refl = new \ReflectionClass($this);
         $fname = $refl->getFileName();
-        $kernelDir = \dirname($fname);
 
-        return $kernelDir;
+        return \dirname($fname);
     }
 
     public function getCacheDir(): string
     {
         return implode('/', [
-            $this->getKernelDir(),
+            $this->getProjectDir(),
             'var',
             'cache',
         ]);
@@ -192,7 +188,7 @@ public function getLogDir(): string
     /**
      * Registers the bundles defined in config/bundles.php.
      */
-    protected function registerConfiguredBundles()
+    protected function registerConfiguredBundles(): void
     {
         $bundleFilePath = $this->getKernelDir().'/config/bundles.php';
         if (!file_exists($bundleFilePath)) {
diff --git a/tests/Fixtures/TestTestCase.php b/tests/Fixtures/TestTestCase.php
index ca96891..17b2b4c 100644
--- a/tests/Fixtures/TestTestCase.php
+++ b/tests/Fixtures/TestTestCase.php
@@ -16,7 +16,7 @@
 
 class TestTestCase extends BaseTestCase
 {
-    public function setKernel(KernelInterface $kernel)
+    public function setKernel(KernelInterface $kernel): void
     {
         static::$kernel = $kernel;
     }
diff --git a/tests/Functional/BaseTestCaseTest.php b/tests/Functional/BaseTestCaseTest.php
index 34ad8c3..dbfaa8c 100644
--- a/tests/Functional/BaseTestCaseTest.php
+++ b/tests/Functional/BaseTestCaseTest.php
@@ -25,25 +25,10 @@
 
 class BaseTestCaseTest extends TestCase
 {
-    /**
-     * @var Container&MockObject
-     */
-    private $container;
-
-    /**
-     * @var KernelInterface&MockObject
-     */
-    private $kernel;
-
-    /**
-     * @var TestTestCase
-     */
-    private $testCase;
-
-    /**
-     * @var KernelBrowser&MockObject
-     */
-    private $client;
+    private Container&MockObject $container;
+    private KernelInterface&MockObject $kernel;
+    private TestTestCase $testCase;
+    private KernelBrowser&MockObject $client;
 
     protected function setUp(): void
     {
@@ -99,7 +84,7 @@ public function testItCanProvideAFrameworkBundleClient(): void
         $this->assertInstanceOf(KernelBrowser::class, $method->invoke($this->testCase));
     }
 
-    public function provideTestDb()
+    public function provideTestDb(): array
     {
         return [
             ['PHPCR', 'PHPCR'],
@@ -112,7 +97,7 @@ public function provideTestDb()
     /**
      * @dataProvider provideTestDb
      */
-    public function testDb($dbName, $expected)
+    public function testDb(string $dbName, string|null $expected): void
     {
         $class = new \ReflectionClass(BaseTestCase::class);
         $method = $class->getMethod('getDbManager');
diff --git a/tests/Functional/HttpKernel/TestKernelTest.php b/tests/Functional/HttpKernel/TestKernelTest.php
index 775ce19..4d67acc 100644
--- a/tests/Functional/HttpKernel/TestKernelTest.php
+++ b/tests/Functional/HttpKernel/TestKernelTest.php
@@ -9,10 +9,11 @@
  * file that was distributed with this source code.
  */
 
-namespace Symfony\Cmf\Component\Testing\Tests\HttpKernel;
+namespace Symfony\Cmf\Component\Testing\Tests\Functional\HttpKernel;
 
 use Doctrine\Bundle\DoctrineBundle\DoctrineBundle;
 use Doctrine\Bundle\PHPCRBundle\DoctrinePHPCRBundle;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
 use Symfony\Bundle\FrameworkBundle\FrameworkBundle;
 use Symfony\Bundle\SecurityBundle\SecurityBundle;
@@ -22,12 +23,9 @@
 
 class TestKernelTest extends TestCase
 {
-    /**
-     * @var TestKernel
-     */
-    private $kernel;
+    private TestKernel&MockObject $kernel;
 
-    private $mockBundle;
+    private BundleInterface&MockObject $mockBundle;
 
     protected function setUp(): void
     {
@@ -41,7 +39,7 @@ protected function setUp(): void
     /**
      * @dataProvider bundleSetProvider
      */
-    public function testBundleSetRequire(array $bundleSets, array $expectedBundles)
+    public function testBundleSetRequire(array $bundleSets, array $expectedBundles): void
     {
         $this->kernel->requireBundleSets($bundleSets);
         $bundles = array_keys($this->kernel->registerBundles());
@@ -52,7 +50,7 @@ public function testBundleSetRequire(array $bundleSets, array $expectedBundles)
         }
     }
 
-    public function bundleSetProvider()
+    public function bundleSetProvider(): array
     {
         return [
             [['default'], [FrameworkBundle::class, SecurityBundle::class, TwigBundle::class]],
@@ -61,7 +59,7 @@ public function bundleSetProvider()
         ];
     }
 
-    public function testBundleAdd()
+    public function testBundleAdd(): void
     {
         $this->kernel->addBundle($this->mockBundle);
         $this->kernel->addBundle($this->mockBundle);
@@ -69,7 +67,7 @@ public function testBundleAdd()
         $this->assertCount(2, $this->kernel->registerBundles());
     }
 
-    public function testRequireInvalidBundleSet()
+    public function testRequireInvalidBundleSet(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $this->kernel->requireBundleSet('foobar');
diff --git a/tests/Unit/Constraint/SchemaAcceptsXmlTest.php b/tests/Unit/Constraint/SchemaAcceptsXmlTest.php
index 898de98..91b2b7b 100644
--- a/tests/Unit/Constraint/SchemaAcceptsXmlTest.php
+++ b/tests/Unit/Constraint/SchemaAcceptsXmlTest.php
@@ -16,7 +16,7 @@
 
 class SchemaAcceptsXmlTest extends TestCase
 {
-    public function testCount()
+    public function testCount(): void
     {
         $constraint = new SchemaAcceptsXml(['config1', 'config2', 'config3']);
 
@@ -31,7 +31,7 @@ public function testCount()
     /**
      * @dataProvider getAssertingData
      */
-    public function testAsserting($input, $schemaFile, $result, $message = null)
+    public function testAsserting($input, $schemaFile, $result, $message = null): void
     {
         $constraint = new SchemaAcceptsXml($input);
 
@@ -47,7 +47,7 @@ public function testAsserting($input, $schemaFile, $result, $message = null)
         }
     }
 
-    public function getAssertingData()
+    public function getAssertingData(): array
     {
         $schema1 = __DIR__.'/../../Fixtures/schema/schema1.xsd';
 
@@ -68,7 +68,7 @@ public function getAssertingData()
         return $data;
     }
 
-    public function testFailsIfNoConfigElementIsAvailable()
+    public function testFailsIfNoConfigElementIsAvailable(): void
     {
         $dom = new \DOMDocument();
         $dom->loadXML('<container></container>');
diff --git a/tests/Unit/XmlSchemaTestCaseTest.php b/tests/Unit/XmlSchemaTestCaseTest.php
index d02ea45..ea13d7f 100644
--- a/tests/Unit/XmlSchemaTestCaseTest.php
+++ b/tests/Unit/XmlSchemaTestCaseTest.php
@@ -15,14 +15,14 @@
 
 class XmlSchemaTestCaseTest extends XmlSchemaTestCase
 {
-    public function testAcceptsSingleDomsWithoutArray()
+    public function testAcceptsSingleDomsWithoutArray(): void
     {
         $dom = new \DOMDocument();
         $dom->loadXML('<container><config xmlns="http://cmf.symfony.com/schema/dic/foo" required="f"/></container>');
         $this->assertSchemaAcceptsXml($dom, __DIR__.'/../Fixtures/schema/schema1.xsd');
     }
 
-    public function testNegativeAssertion()
+    public function testNegativeAssertion(): void
     {
         $dom = new \DOMDocument();
         $dom->loadXML('<container><config xmlns="http://cmf.symfony.com/schema/dic/foo" /></container>');