diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..a6f1eac
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,11 @@
+# Exclude from release archives
+/.github export-ignore
+/Tests export-ignore
+.gitattributes export-ignore
+.gitignore export-ignore
+grumphp.yml export-ignore
+Makefile export-ignore
+phpstan.neon export-ignore
+phpstan-baseline.neon export-ignore
+phpunit.xml export-ignore
+rector.php export-ignore
diff --git a/.github/workflows/tasks.yml b/.github/workflows/tasks.yml
index ac43d24..a9c7b7e 100644
--- a/.github/workflows/tasks.yml
+++ b/.github/workflows/tasks.yml
@@ -9,25 +9,21 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: [ '8.1', '8.2', '8.3', '8.4' ]
-        typo3: [ '11', '12', '13' ]
-        exclude:
-          - php: '8.1'
-            typo3: '13'
-          - php: '8.4'
-            typo3: '11'
+        php: [ '82', '83', '84' ]
+        typo3: [ '12', '13' ]
+    container:
+      image: ghcr.io/typo3/core-testing-php${{ matrix.php }}:latest
     steps:
-      - name: Setup PHP with PECL extension
-        uses: shivammathur/setup-php@v2
-        with:
-          php-version: ${{ matrix.php }}
+      - name: Install dependencies
+        run: apk add --no-cache nodejs
       - uses: actions/checkout@v5
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         with:
           path: ~/.composer/cache/files
           key: ${{ runner.os }}-${{ matrix.php }}-composer-${{ hashFiles('**/composer.lock') }}
           restore-keys: |
             ${{ runner.os }}-${{ matrix.php }}-composer-
-      - run: composer require typo3/minimal="^${{ matrix.typo3 }}" --dev
-      - run: composer install --no-interaction --no-progress
-      - run: ./vendor/bin/grumphp run --ansi
+      - run: git config --global --add safe.directory $GITHUB_WORKSPACE
+      - run: composer switchto${{ matrix.typo3 }}
+      - run: ./vendor/bin/grumphp run --ansi --no-interaction
+      - run: composer test
diff --git a/.gitignore b/.gitignore
index 0c7c416..b1220e8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@ vendor
 public
 composer.lock
 var/
+.phpunit.result.cache
diff --git a/Classes/EventListener/RenderedEventListener.php b/Classes/EventListener/RenderedEventListener.php
index a8a368b..7478d5e 100644
--- a/Classes/EventListener/RenderedEventListener.php
+++ b/Classes/EventListener/RenderedEventListener.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Pluswerk\PlusMinify\EventListener;
 
 use AUS\SsiInclude\Event\RenderedEvent;
diff --git a/Configuration/RequestMiddlewares.php b/Configuration/RequestMiddlewares.php
index 685c466..e7e57dd 100644
--- a/Configuration/RequestMiddlewares.php
+++ b/Configuration/RequestMiddlewares.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Pluswerk\PlusMinify\Middleware\MinifyMiddleware;
 
 return [
diff --git a/Configuration/Services.yaml b/Configuration/Services.yaml
index d1adcd0..f2a63a0 100644
--- a/Configuration/Services.yaml
+++ b/Configuration/Services.yaml
@@ -4,6 +4,9 @@ services:
     autoconfigure: true
     public: false
 
+  Pluswerk\PlusMinify\:
+    resource: '../Classes/*'
+
   Pluswerk\PlusMinify\EventListener\RenderedEventListener:
     tags:
       - name: event.listener
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..5277b70
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,41 @@
+ACT_IMAGE ?= efrecon/act:v0.2.80
+WORKDIR   ?= /work
+UID_GID    := $(shell id -u):$(shell id -g)
+DOCKER_GID := $(shell stat -c '%g' /var/run/docker.sock)
+
+PLATFORM  ?= -P ubuntu-latest=ghcr.io/catthehacker/ubuntu:act-24.04
+
+# Secrets-File in ENV format
+SECRETS   ?= --secret-file .secrets
+
+ACT_ARGS ?= \
+  --artifact-server-path /home/act/.cache/artifacts
+
+define DOCKER_RUN
+docker run --rm -it \
+  -u $(UID_GID) \
+  --group-add $(DOCKER_GID) \
+  -e HOME=/home/act \
+  -e XDG_CACHE_HOME=/home/act/.cache \
+  -e ACT_CACHE_DIR=/home/act/.cache/actcache \
+  -v /var/run/docker.sock:/var/run/docker.sock \
+  -v $(PWD):$(WORKDIR) -w $(WORKDIR) \
+  -v $$HOME/.cache:/home/act/.cache \
+  $(ACT_IMAGE)
+endef
+
+# ---- Targets ----
+.PHONY: all ci clean
+
+all: ci clean
+
+ci:   ## Standard-Event "push"
+	$(DOCKER_RUN) $(PLATFORM) $(SECRETS) $(ACT_ARGS) 2>&1 | tee /tmp/act-output.log; \
+	echo ""; \
+	echo "=== 🏁 Summary ==="; \
+	grep "🏁" /tmp/act-output.log || true
+
+
+clean:
+	docker rm -f $$(docker ps -aq --filter "name=act-") 2>/dev/null || true
+
diff --git a/Tests/Unit/Service/MinifyServiceTest.php b/Tests/Unit/Service/MinifyServiceTest.php
new file mode 100644
index 0000000..dc74aff
--- /dev/null
+++ b/Tests/Unit/Service/MinifyServiceTest.php
@@ -0,0 +1,141 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pluswerk\PlusMinify\Tests\Unit\Service;
+
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+use Pluswerk\PlusMinify\Service\MinifyService;
+
+class MinifyServiceTest extends TestCase
+{
+    private MinifyService $subject;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        // Reset all minify feature flags — everything disabled by default
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify'] = [];
+
+        $this->subject = new MinifyService();
+    }
+
+    // -------------------------------------------------------------------------
+    // All features off (default)
+    // -------------------------------------------------------------------------
+
+    #[Test]
+    public function minifyKeepsHtmlCommentsWhenNoFeaturesAreEnabled(): void
+    {
+        $html = '<html><head><meta charset="utf-8"><!-- a comment --></head><body><p>Hello</p></body></html>';
+
+        $result = $this->subject->minify($html);
+
+        self::assertStringContainsString('<!-- a comment -->', $result);
+    }
+
+    #[Test]
+    public function minifyKeepsTypo3CommentWhenNoFeaturesAreEnabled(): void
+    {
+        $html = '<html><head><meta charset="utf-8"><!-- TYPO3 page info --></head><body><p>Hello</p></body></html>';
+
+        $result = $this->subject->minify($html);
+
+        self::assertStringContainsString('<!-- TYPO3 page info -->', $result);
+    }
+
+    // -------------------------------------------------------------------------
+    // remove_comments alone — comment removal needs the DOM parser too,
+    // so the output stays unchanged when only remove_comments is set.
+    // -------------------------------------------------------------------------
+
+    #[Test]
+    public function minifyDoesNotRemoveCommentsWithOnlyRemoveCommentsFlagEnabled(): void
+    {
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['remove_comments'] = '1';
+
+        $html = '<html><head><meta charset="utf-8"></head><body><!-- just a comment --><p>Hello</p></body></html>';
+
+        $result = $this->subject->minify($html);
+
+        // Without the DOM parser the minifier cannot parse the tree,
+        // so the comment is left in the output.
+        self::assertStringContainsString('<!-- just a comment -->', $result);
+    }
+
+    // -------------------------------------------------------------------------
+    // remove_comments + optimize_via_html_dom_parser (the realistic combination)
+    // -------------------------------------------------------------------------
+
+    #[Test]
+    public function minifyRemovesRegularCommentsWhenRemoveCommentsAndDomParserAreEnabled(): void
+    {
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['remove_comments'] = '1';
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['optimize_via_html_dom_parser'] = '1';
+
+        $html = '<html><head><meta charset="utf-8"></head><body><!-- just a comment --><p>Hello</p></body></html>';
+
+        $result = $this->subject->minify($html);
+
+        self::assertStringNotContainsString('<!-- just a comment -->', $result);
+        self::assertStringContainsString('<p>Hello</p>', $result);
+    }
+
+    #[Test]
+    public function minifyPreservesTypo3CommentWhenRemoveCommentsAndDomParserAreEnabled(): void
+    {
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['remove_comments'] = '1';
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['optimize_via_html_dom_parser'] = '1';
+
+        $html = '<html><head><meta charset="utf-8"><!-- TYPO3CMS id=1 --></head><body><p>Hello</p></body></html>';
+
+        $result = $this->subject->minify($html);
+
+        self::assertStringContainsString('<!-- TYPO3CMS id=1 -->', $result);
+    }
+
+    #[Test]
+    public function minifyRemovesRegularCommentButKeepsTypo3CommentWhenBothFlagsAreEnabled(): void
+    {
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['remove_comments'] = '1';
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['optimize_via_html_dom_parser'] = '1';
+
+        $html = '<html><head><meta charset="utf-8"><!-- TYPO3 page --></head><body><!-- drop me --><p>Hello</p></body></html>';
+
+        $result = $this->subject->minify($html);
+
+        self::assertStringContainsString('<!-- TYPO3 page -->', $result);
+        self::assertStringNotContainsString('<!-- drop me -->', $result);
+    }
+
+    // -------------------------------------------------------------------------
+    // Output integrity
+    // -------------------------------------------------------------------------
+
+    #[Test]
+    public function minifyReturnsFallbackHtmlWhenMinifierProducesEmptyString(): void
+    {
+        // An empty string causes the minifier to return '' which triggers
+        // the $originalHtml fallback — the method must not crash.
+        $result = $this->subject->minify('');
+
+        self::assertSame('', $result);
+    }
+
+    #[Test]
+    public function minifyAppendsClosingBodyTagWhenAbsentFromMinifiedOutput(): void
+    {
+        // Enable features that actually cause HtmlMin to strip closing tags.
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['remove_comments'] = '1';
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['optimize_via_html_dom_parser'] = '1';
+        $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['minify']['remove_omitted_html_tags'] = '1';
+
+        $html = '<html><head><meta charset="utf-8"></head><body><p>Hello</p></body></html>';
+
+        $result = $this->subject->minify($html);
+
+        self::assertStringEndsWith('</body>', $result);
+    }
+}
diff --git a/composer.json b/composer.json
index 2072b57..ebaafdb 100644
--- a/composer.json
+++ b/composer.json
@@ -8,22 +8,28 @@
     "source": "https://github.com/pluswerk/minify"
   },
   "require": {
-    "php": "~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0",
+    "php": "~8.2.0 || ~8.3.0 || ~8.4.0 || ~8.5.0",
     "composer-runtime-api": "^2",
-    "typo3/cms-core": "^11.5 || ^12.4 || ^13.4",
-    "voku/html-min": "^4.5.1"
+    "typo3/cms-core": "^12.4 || ^13.4",
+    "voku/html-min": "^5.0.0"
   },
   "require-dev": {
     "andersundsehr/ssi-include": "^1.1.0 || ^2.2.0",
     "pluswerk/grumphp-config": "^7 || ^10",
-    "saschaegerer/phpstan-typo3": "^1.10.0 || ^2.1.1",
-    "ssch/typo3-rector": "^2.5.0 || ^3.6.2"
+    "saschaegerer/phpstan-typo3": "^1.10.2 || ^2.1.1",
+    "ssch/typo3-rector": "^2.15.2 || ^3.14.1",
+    "typo3/testing-framework": "^8.2 || ^9.4"
   },
   "autoload": {
     "psr-4": {
       "Pluswerk\\PlusMinify\\": "Classes/"
     }
   },
+  "autoload-dev": {
+    "psr-4": {
+      "Pluswerk\\PlusMinify\\Tests\\": "Tests/"
+    }
+  },
   "config": {
     "allow-plugins": {
       "ergebnis/composer-normalize": true,
@@ -39,5 +45,16 @@
     "typo3/cms": {
       "extension-key": "minify"
     }
+  },
+  "scripts": {
+    "switchto12": [
+      "rm -rf composer.lock vendor/composer/installed.json",
+      "@composer req typo3/minimal:^12 --dev --no-interaction --no-progress"
+    ],
+    "switchto13": [
+      "rm -rf composer.lock vendor/composer/installed.json",
+      "@composer req typo3/minimal:^13 --dev --no-interaction --no-progress"
+    ],
+    "test": "@php ./vendor/bin/phpunit --testdox --stderr"
   }
 }
diff --git a/ext_emconf.php b/ext_emconf.php
deleted file mode 100644
index 5ff53a8..0000000
--- a/ext_emconf.php
+++ /dev/null
@@ -1,21 +0,0 @@
-<?php
-
-use Composer\InstalledVersions;
-
-/** @var string $_EXTKEY */
-$EM_CONF[$_EXTKEY] = [
-    'title' => '+Pluswerk: Minify',
-    'description' => 'Minifies your html at a glace',
-    'category' => 'service',
-    'author' => 'Stefan Lamm',
-    'author_email' => 'stefan.lamm@pluswerk.ag',
-    'state' => 'stable',
-    'version' => InstalledVersions::getPrettyVersion('pluswerk/minify'),
-    'constraints' => [
-        'depends' => [
-            'typo3' => '11.5.0 - 13.99.99',
-        ],
-        'conflicts' => [],
-        'suggests' => [],
-    ],
-];
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..2f2b108
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.3/phpunit.xsd" bootstrap="vendor/autoload.php" executionOrder="depends,defects" beStrictAboutOutputDuringTests="true" failOnRisky="true" failOnWarning="true">
+    <testsuites>
+        <testsuite name="default">
+            <directory>Tests</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory suffix=".php">Classes</directory>
+        </include>
+    </source>
+</phpunit>