diff --git a/.github/workflows/phpunit.yaml b/.github/workflows/phpunit.yaml
new file mode 100644
index 0000000..22dfdef
--- /dev/null
+++ b/.github/workflows/phpunit.yaml
@@ -0,0 +1,91 @@
+name: PHPUnit
+
+on:
+  pull_request:
+
+jobs:
+  phpunit:
+    name: "PHPUnit - PHP ${{ matrix.php-version }}"
+    runs-on: ubuntu-20.04
+    continue-on-error: false
+    env:
+      SYMFONY_REQUIRE: ${{matrix.symfony-require}}
+      SYMFONY_DEPRECATIONS_HELPER: ${{matrix.symfony-deprecations-helper}}
+
+    strategy:
+      matrix:
+        php-version:
+          - "7.4"
+          - "8.0"
+          - "8.1"
+        deps:
+          - "stable"
+        symfony-require:
+          - "5.4.*"
+        symfony-deprecations-helper:
+          - "5"
+        include:
+          - symfony-require: "4.4.*"
+            php-version: "7.4"
+            deps: "low"
+            symfony-deprecations-helper: ""
+
+          - symfony-require: "4.4.*"
+            php-version: "7.4"
+            deps: "stable"
+            symfony-deprecations-helper: "5"
+
+          - symfony-require: "6.0.*"
+            php-version: "8.0"
+            deps: "stable"
+            symfony-deprecations-helper: "5"
+
+          - symfony-require: "6.0.*"
+            php-version: "8.1"
+            deps: "stable"
+            symfony-deprecations-helper: "5"
+
+      fail-fast: true
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install PHP with extensions
+        uses: shivammathur/setup-php@v2
+        with:
+          coverage: none
+          php-version: ${{ matrix.php-version }}
+          extensions: mbstring, intl, pdo, pdo_sqlite, sqlite3
+          ini-values: date.timezone=UTC
+
+      - name: Validate composer.json and composer.lock
+        run: composer validate --strict
+
+      - name: Install dependencies with Composer
+        run: composer update --no-interaction --prefer-dist --optimize-autoloader --prefer-stable
+
+      - name: Cache dependencies installed with Composer
+        uses: actions/cache@v2
+        with:
+          path: ~/.composer/cache
+          key: "php-${{ matrix.php-version }}-composer-locked-${{ hashFiles('composer.lock') }}"
+          restore-keys: "php-${{ matrix.php-version }}-composer-locked-"
+
+      - name: Install stable dependencies with Composer
+        run: composer update --no-interaction --prefer-dist --prefer-stable
+        if: "${{ matrix.deps == 'stable' }}"
+
+      - name: Install dev dependencies with Composer
+        run: composer update --no-interaction --prefer-dist
+        if: "${{ matrix.deps == 'dev' }}"
+
+      - name: Install lowest possible dependencies with Composer
+        run: composer update --no-interaction --prefer-dist --prefer-stable --prefer-lowest
+        if: "${{ matrix.deps == 'low' }}"
+
+      - name: Install PHPUnit
+        run: composer run-script test install
+
+      - name: Run tests
+        run: composer run-script test -v
diff --git a/.gitignore b/.gitignore
index d2cb556..717b31c 100755
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,6 @@
+.phpunit.result.cache
 phpunit.xml
+var/
 vendor/*
 composer.lock
 Tests/fixtures/app/cache
diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 90bbdfa..c9b6e90 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -12,11 +12,10 @@ class Configuration implements ConfigurationInterface
      *
      * @return TreeBuilder
      */
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder('knp_markdown');
-        // BC layer for symfony/config < 4.2
-        $rootNode = method_exists($treeBuilder, 'getRootNode') ? $treeBuilder->getRootNode() : $treeBuilder->root('knp_markdown');
+        $rootNode = $treeBuilder->getRootNode();
 
         $rootNode
             ->addDefaultsIfNotSet()
diff --git a/Helper/MarkdownHelper.php b/Helper/MarkdownHelper.php
index 0b3974f..fc7de2d 100644
--- a/Helper/MarkdownHelper.php
+++ b/Helper/MarkdownHelper.php
@@ -50,7 +50,7 @@ class MarkdownHelper implements HelperInterface
      *
      * @return string The default charset
      */
-    public function getCharset()
+    public function getCharset(): string
     {
         return $this->charset;
     }
diff --git a/Parser/MarkdownParser.php b/Parser/MarkdownParser.php
index df369b3..378786a 100644
--- a/Parser/MarkdownParser.php
+++ b/Parser/MarkdownParser.php
@@ -124,7 +124,7 @@ class MarkdownParser extends MarkdownExtra implements MarkdownParserInterface
     /**
      * Simplify detab
      */
-    public function detab($text)
+    public function detab($text): string
     {
         return str_replace("\t", str_repeat(' ', $this->tab_width), $text);
     }
diff --git a/Parser/Preset/Min.php b/Parser/Preset/Min.php
index 2a4646b..50f774f 100644
--- a/Parser/Preset/Min.php
+++ b/Parser/Preset/Min.php
@@ -15,7 +15,7 @@ class Min extends MarkdownParser
             $this->features[$name] = false;
         }
 
-        return parent::__construct($features);
+        parent::__construct($features);
     }
 }
 
diff --git a/README.markdown b/README.markdown
index 715d6ad..398d3a7 100644
--- a/README.markdown
+++ b/README.markdown
@@ -2,6 +2,9 @@ Provide markdown conversion (based on [Michel Fortin work](https://github.com/mi
 
 [![Build Status](https://secure.travis-ci.org/KnpLabs/KnpMarkdownBundle.svg)](http://travis-ci.org/KnpLabs/KnpMarkdownBundle)
 
+![ci.yml](https://github.com/tacman/KnpMarkdownBundle/actions/workflows/ci.yml/badge.svg)
+![php.yml](https://github.com/tacman/KnpMarkdownBundle/actions/workflows/php.yml/badge.svg)
+
 ## INSTALLATION
 
 Add KnpMarkdownBundle to your project via [Composer](https://getcomposer.org/):
diff --git a/Twig/Extension/MarkdownTwigExtension.php b/Twig/Extension/MarkdownTwigExtension.php
index e9ab8c0..9d20683 100644
--- a/Twig/Extension/MarkdownTwigExtension.php
+++ b/Twig/Extension/MarkdownTwigExtension.php
@@ -15,19 +15,19 @@ class MarkdownTwigExtension extends AbstractExtension
         $this->parserManager = $parserManager;
     }
 
-    public function getFilters()
+    public function getFilters(): array
     {
         return array(
             new TwigFilter('markdown', array($this, 'markdown'), array('is_safe' => array('html'))),
         );
     }
 
-    public function markdown($text, $parser = null)
+    public function markdown($text, $parser = null): string
     {
         return $this->parserManager->transform($text, $parser);
     }
 
-    public function getName()
+    public function getName(): string
     {
         return 'markdown';
     }
diff --git a/composer.json b/composer.json
index 961801c..c064cb9 100644
--- a/composer.json
+++ b/composer.json
@@ -18,14 +18,16 @@
     ],
 
     "require": {
-        "php":                      "^7.1.3|^8.0",
-        "symfony/framework-bundle": "~3.4|^4.0|^5.0",
-        "symfony/dependency-injection": "~3.4|^4.0|^5.0",
-        "michelf/php-markdown":     "~1.4"
+        "php": "^7.4|^8.0",
+        "symfony/framework-bundle": "^4.4|^5.0|^6.0",
+        "symfony/dependency-injection": "^4.4|^5.0|^6.0",
+        "michelf/php-markdown": "^1.9"
     },
     "require-dev": {
-        "symfony/phpunit-bridge": "^4.4.0 || ^5.0",
-        "symfony/templating": "~3.4|^4.0|^5.0"
+        "symfony/phpunit-bridge": "^4.4.11|^5.0|^6.0",
+        "symfony/templating": "^4.4|^5.0|^6.0",
+        "phpstan/phpstan": "^1.2",
+        "phpstan/phpstan-symfony": "^1.0"
     },
     "suggest": {
         "symfony/twig-bundle": "to use the Twig markdown filter",
@@ -38,6 +40,18 @@
         }
     },
 
+    "scripts": {
+        "test": [
+            "php ./vendor/bin/simple-phpunit"
+        ]
+    },
+
+    "autoload-dev": {
+        "psr-4": {
+            "Knp\\Bundle\\MarkdownBundle\\Tests\\": "tests/"
+        }
+    },
+
     "autoload": {
         "psr-4": {
             "Knp\\Bundle\\MarkdownBundle\\": ""
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 0bdd033..e8fcfce 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -2,30 +2,30 @@
 
 <!-- http://phpunit.de/manual/4.1/en/appendixes.configuration.html -->
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/6.3/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
          backupGlobals="false"
          bootstrap="vendor/autoload.php"
          colors="true"
          failOnRisky="true"
          failOnWarning="true"
+         failOnIncomplete="false"
 >
     <php>
-        <server name="SYMFONY_PHPUNIT_VERSION" value="7.5" />
+        <server name="SYMFONY_PHPUNIT_VERSION" value="9.5" />
     </php>
 
+    <coverage processUncoveredFiles="true">
+      <include>
+          <directory>.</directory>
+      </include>
+      <exclude>
+          <directory>tests</directory>
+          <directory>vendor</directory>
+      </exclude>
+    </coverage>
     <testsuites>
         <testsuite name="Markdown Test Suite">
             <directory>tests</directory>
         </testsuite>
     </testsuites>
-
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory>.</directory>
-            <exclude>
-                <directory>tests</directory>
-                <directory>vendor</directory>
-            </exclude>
-        </whitelist>
-    </filter>
-</phpunit>
\ No newline at end of file
+</phpunit>
diff --git a/Tests/EscapingTest.php b/tests/EscapingTest.php
similarity index 89%
rename from Tests/EscapingTest.php
rename to tests/EscapingTest.php
index a2d396f..443eec1 100644
--- a/Tests/EscapingTest.php
+++ b/tests/EscapingTest.php
@@ -2,13 +2,14 @@
 
 namespace Knp\Bundle\MarkdownBundle\Tests;
 
+use PHPUnit\Framework\TestCase;
 use Knp\Bundle\MarkdownBundle\Parser\MarkdownParser as Parser;
 
-class EscapingTest extends \PHPUnit_Framework_TestCase
+class EscapingTest extends TestCase
 {
     protected $parser;
 
-    public function setUp()
+    protected function setUp(): void
     {
         $this->parser = new Parser();
     }
diff --git a/Tests/FeatureTest.php b/tests/FeatureTest.php
similarity index 97%
rename from Tests/FeatureTest.php
rename to tests/FeatureTest.php
index 7c0d099..a2291d7 100644
--- a/Tests/FeatureTest.php
+++ b/tests/FeatureTest.php
@@ -3,8 +3,9 @@
 namespace Knp\Bundle\MarkdownBundle\Tests;
 
 use Knp\Bundle\MarkdownBundle\Parser\MarkdownParser as Parser;
+use PHPUnit\Framework\TestCase;
 
-class FeatureTest extends \PHPUnit_Framework_TestCase
+class FeatureTest extends TestCase
 {
     public function testParser()
     {
@@ -754,10 +755,10 @@ EOF;
         // asserting a few things instead of comparing full final HTML
         // because a few minor things have changed over versions of Michelf
         // With assertContains(), tests will pass across all versions
-        $this->assertContains('<p>That\'s some text with a footnote.<sup id="fnref:1"><a href="#fn:1"', $actualHtml);
-        $this->assertContains('<div class="footnotes"', $actualHtml);
-        $this->assertContains('<li id="fn:1"', $actualHtml);
-        $this->assertContains('<p>And that\'s the footnote.&#160;<a href="#fnref:1" class="footnote-backref"', $actualHtml);
+        $this->assertStringContainsString('<p>That\'s some text with a footnote.<sup id="fnref:1"><a href="#fn:1"', $actualHtml);
+        $this->assertStringContainsString('<div class="footnotes"', $actualHtml);
+        $this->assertStringContainsString('<li id="fn:1"', $actualHtml);
+        $this->assertStringContainsString('<p>And that\'s the footnote.&#160;<a href="#fnref:1" class="footnote-backref"', $actualHtml);
     }
 
     /**
diff --git a/Tests/IntegrationTest.php b/tests/IntegrationTest.php
similarity index 73%
rename from Tests/IntegrationTest.php
rename to tests/IntegrationTest.php
index 4586e54..d86dee4 100644
--- a/Tests/IntegrationTest.php
+++ b/tests/IntegrationTest.php
@@ -4,14 +4,16 @@ namespace Knp\Bundle\MarkdownBundle\Tests;
 
 use Knp\Bundle\MarkdownBundle\KnpMarkdownBundle;
 use Knp\Bundle\MarkdownBundle\Parser\MarkdownParser;
+use PHPUnit\Framework\TestCase;
 use Symfony\Bundle\FrameworkBundle\FrameworkBundle;
 use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
 use Symfony\Component\Config\Loader\LoaderInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\HttpKernel\Kernel;
+use Symfony\Component\Routing\Loader\Configurator\RoutingConfigurator;
 use Symfony\Component\Routing\RouteCollectionBuilder;
 
-class IntegrationTest extends \PHPUnit_Framework_TestCase
+class IntegrationTest extends TestCase
 {
     public function testServicesAvailable()
     {
@@ -29,7 +31,7 @@ class IntegrationKernel extends Kernel
 
     private $cacheDir;
 
-    public function registerBundles()
+    public function registerBundles(): iterable
     {
         return [
             new FrameworkBundle(),
@@ -37,16 +39,20 @@ class IntegrationKernel extends Kernel
         ];
     }
 
-    protected function configureRoutes(RouteCollectionBuilder $routes)
+    protected function configureRoutes(RoutingConfigurator $routes)
     {
     }
 
     protected function configureContainer(ContainerBuilder $c, LoaderInterface $loader)
     {
-        $c->setParameter('kernel.secret', '1234');
+
+            $c->loadFromExtension('framework', [
+                'secret' => 'F00',
+                'router' => ['utf8' => true]
+            ]);
     }
 
-    public function getCacheDir()
+    public function getCacheDir(): string
     {
         if (null === $this->cacheDir) {
             $this->cacheDir = sys_get_temp_dir().'/'.rand(100, 999);
diff --git a/Tests/Parser/ParserManagerTest.php b/tests/Parser/ParserManagerTest.php
similarity index 92%
rename from Tests/Parser/ParserManagerTest.php
rename to tests/Parser/ParserManagerTest.php
index 9285ea8..7357c1e 100644
--- a/Tests/Parser/ParserManagerTest.php
+++ b/tests/Parser/ParserManagerTest.php
@@ -5,8 +5,9 @@ namespace Knp\Bundle\MarkdownBundle\Tests\Parser;
 use Knp\Bundle\MarkdownBundle\Helper\MarkdownHelper;
 use Knp\Bundle\MarkdownBundle\Tests\fixtures\app\TestKernel;
 use Knp\Bundle\MarkdownBundle\Parser\ParserManager;
+use PHPUnit\Framework\TestCase;
 
-class ParserManagerTest extends \PHPUnit_Framework_TestCase
+class ParserManagerTest extends TestCase
 {
     public function testIntegration()
     {
diff --git a/Tests/Performance/.htaccess b/tests/Performance/.htaccess
similarity index 100%
rename from Tests/Performance/.htaccess
rename to tests/Performance/.htaccess
diff --git a/Tests/Performance/Base.php b/tests/Performance/Base.php
similarity index 100%
rename from Tests/Performance/Base.php
rename to tests/Performance/Base.php
diff --git a/Tests/Performance/Light.php b/tests/Performance/Light.php
similarity index 100%
rename from Tests/Performance/Light.php
rename to tests/Performance/Light.php
diff --git a/Tests/Performance/Max.php b/tests/Performance/Max.php
similarity index 100%
rename from Tests/Performance/Max.php
rename to tests/Performance/Max.php
diff --git a/Tests/Performance/Medium.php b/tests/Performance/Medium.php
similarity index 100%
rename from Tests/Performance/Medium.php
rename to tests/Performance/Medium.php
diff --git a/Tests/Performance/Min.php b/tests/Performance/Min.php
similarity index 100%
rename from Tests/Performance/Min.php
rename to tests/Performance/Min.php
diff --git a/Tests/Performance/index.php b/tests/Performance/index.php
similarity index 100%
rename from Tests/Performance/index.php
rename to tests/Performance/index.php
diff --git a/Tests/Performance/run b/tests/Performance/run
similarity index 100%
rename from Tests/Performance/run
rename to tests/Performance/run
diff --git a/Tests/PresetTest.php b/tests/PresetTest.php
similarity index 94%
rename from Tests/PresetTest.php
rename to tests/PresetTest.php
index cc7aaf0..224cb31 100644
--- a/Tests/PresetTest.php
+++ b/tests/PresetTest.php
@@ -3,8 +3,9 @@
 namespace Knp\Bundle\MarkdownBundle\Tests;
 
 use Knp\Bundle\MarkdownBundle\Parser\Preset as Preset;
+use PHPUnit\Framework\TestCase;
 
-class PresetTest extends \PHPUnit_Framework_TestCase
+class PresetTest extends TestCase
 {
     public function testMax()
     {
diff --git a/Tests/fixtures/app/TestKernel.php b/tests/fixtures/app/TestKernel.php
similarity index 95%
rename from Tests/fixtures/app/TestKernel.php
rename to tests/fixtures/app/TestKernel.php
index b5cb93d..26cf034 100644
--- a/Tests/fixtures/app/TestKernel.php
+++ b/tests/fixtures/app/TestKernel.php
@@ -12,7 +12,7 @@ use Symfony\Component\HttpKernel\Kernel;
 
 class TestKernel extends Kernel
 {
-    public function registerBundles()
+    public function registerBundles(): iterable
     {
         return array(
             new FrameworkBundle(),
@@ -31,4 +31,4 @@ class TestKernel extends Kernel
             $c->setAlias('markdown.parser.parser_manager.public', new Alias('markdown.parser.parser_manager', true));
         });
     }
-}
\ No newline at end of file
+}
diff --git a/Tests/fixtures/big_text.html b/tests/fixtures/big_text.html
similarity index 100%
rename from Tests/fixtures/big_text.html
rename to tests/fixtures/big_text.html
diff --git a/Tests/fixtures/big_text.markdown b/tests/fixtures/big_text.markdown
similarity index 100%
rename from Tests/fixtures/big_text.markdown
rename to tests/fixtures/big_text.markdown