diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..3199cf1
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,42 @@
+name: Test
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    name: Test with PHP ${{ matrix.php-versions }}
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        php-versions: [8.1, 8.2, 8.3] # TODO - Add 8.4 once all tools/dependencies support it
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-versions }}
+
+      - name: Install dependencies
+        uses: ramsey/composer-install@v3
+
+      - name: Run PHP-CS-Fixer
+        run: composer phpcs:check
+
+      - name: Run PHPStan
+        run: composer phpstan
+
+      - name: Run PHPUnit
+        run: composer test
diff --git a/.gitignore b/.gitignore
index 2942141..77387d8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,12 @@
 .idea/
 composer.lock
 vendor/
+
+###> friendsofphp/php-cs-fixer ###
+/.php-cs-fixer.cache
+###< friendsofphp/php-cs-fixer ###
+
+###> phpunit/phpunit ###
+/phpunit.xml
+/.phpunit.cache
+###< phpunit/phpunit ###
diff --git a/.php-cs-fixer.php b/.php-cs-fixer.php
new file mode 100644
index 0000000..70b81c3
--- /dev/null
+++ b/.php-cs-fixer.php
@@ -0,0 +1,35 @@
+<?php
+
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
+use PhpCsFixer\Runner\Parallel\ParallelConfigFactory;
+
+$finder = (new PhpCsFixer\Finder())
+    ->in(__DIR__);
+
+return (new PhpCsFixer\Config())
+    ->setParallelConfig(ParallelConfigFactory::detect())
+    ->setRules([
+        '@PHP81Migration' => true,
+        '@Symfony' => true,
+        '@Symfony:risky' => true,
+        'declare_strict_types' => true,
+        'header_comment' => [
+            'header' => 'Copyright (c) Fusonic GmbH. All rights reserved.'.\PHP_EOL.'Licensed under the MIT License. '.
+                'See LICENSE file in the project root for license information.',
+            'location' => 'after_open',
+        ],
+        'no_useless_else' => true,
+        'no_useless_return' => true,
+        'php_unit_strict' => true,
+        'single_line_throw' => false,
+        'strict_comparison' => true,
+        'strict_param' => true,
+    ])
+    ->setFinder($finder)
+    ->setRiskyAllowed(true);
diff --git a/.scrutinizer.yml b/.scrutinizer.yml
deleted file mode 100644
index 30a9fcf..0000000
--- a/.scrutinizer.yml
+++ /dev/null
@@ -1,17 +0,0 @@
-build:
-  environment:
-    php:
-      version: 7.4
-  tests:
-    override:
-      -
-        command: 'vendor/bin/phpunit --coverage-clover coverage-report'
-        coverage:
-          file: 'coverage-report'
-          format: 'clover'
-
-tools:
-  php_code_sniffer:
-    enabled: true
-    config:
-      standard: PSR2
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 6dcf4bd..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,6 +0,0 @@
-language: php
-php:
-  - 7.4
-  - 8.0
-install: composer install
-script: vendor/bin/phpunit
diff --git a/CHANGELOG.md b/CHANGELOG-2.x.md
similarity index 100%
rename from CHANGELOG.md
rename to CHANGELOG-2.x.md
diff --git a/CHANGELOG-3.x.md b/CHANGELOG-3.x.md
new file mode 100644
index 0000000..dd7cff8
--- /dev/null
+++ b/CHANGELOG-3.x.md
@@ -0,0 +1,16 @@
+# CHANGELOG for 3.x
+
+## 3.0.0
+
+- Bumped the required PHP version from `^7.4 || ^8.0` to `^8.1`
+- Bumped the compatible Symfony version from `^3.0 || ^4.0 || ^5.0 || ^6.0` to `^5.4 || ^6.4 || ^7.1`
+- Upgraded PHPUnit from `^9.0` to `^11.4` and updated tests accordingly
+  - Added `composer test` script for running tests
+- Installed `friendsofphp/php-cs-fixer` and applied Fusonic's code style
+  - Added `composer phpcs:check` script for validating code style
+  - Added `composer phpcs:fix` script for fixing code style violations
+- Installed `phpstan/phpstan`, `phpstan/phpstan-deprecation-rules`, `phpstan/phpstan-phpunit` and
+  `phpstan/phpstan-strict-rules` and fixed reported errors
+  - Added `composer phpstan` script for validating code
+- Updated documentation
+- Switched to GitHub actions for automated testing
diff --git a/LICENSE b/LICENSE
index 46c173a..bb8f68c 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2014 Fusonic GmbH (http://www.fusonic.net)
+Copyright (c) 2014-2024 Fusonic GmbH (https://www.fusonic.net)
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
diff --git a/README.md b/README.md
index b256cac..11e8acf 100644
--- a/README.md
+++ b/README.md
@@ -1,59 +1,64 @@
 # fusonic/opengraph
 
-[![Latest Stable Version](https://poser.pugx.org/fusonic/opengraph/v/stable)](https://packagist.org/packages/fusonic/opengraph)
-[![Total Downloads](https://poser.pugx.org/fusonic/opengraph/downloads)](https://packagist.org/packages/fusonic/opengraph)
-[![Build Status](https://api.travis-ci.org/fusonic/opengraph.svg)](https://travis-ci.org/fusonic/opengraph)
-[![License](https://poser.pugx.org/fusonic/opengraph/license)](https://packagist.org/packages/fusonic/opengraph)
+[![GitHub Release](https://img.shields.io/github/v/release/fusonic/opengraph)](https://github.com/fusonic/opengraph/releases/latest)
+[![Packagist Downloads](https://img.shields.io/packagist/dt/fusonic/opengraph?color=blue)](https://packagist.org/packages/fusonic/opengraph)
+[![Packagist License](https://img.shields.io/packagist/l/fusonic/opengraph)](https://github.com/fusonic/opengraph/blob/master/LICENSE)
+[![GitHub Actions Workflow Status](https://img.shields.io/github/actions/workflow/status/fusonic/opengraph/test)](https://github.com/fusonic/opengraph/actions/workflows/test.yml)
 
-A simple library to read Open Graph data from the web and generate HTML code to publish your own Open Graph objects. A fallback mode enables you to read data from websites that do not implement the Open Graph protocol.
+A simple library to read Open Graph data from the web and generate HTML code to publish your own Open Graph objects. A
+fallback mode enables you to read data from websites that do not implement the Open Graph protocol.
 
-Using this library you can easily retrieve stuff like meta data, video information from YouTube or Vimeo or image information from Flickr without using site-specific APIs since they all implement the Open Graph protocol.
+Using this library you can easily retrieve stuff like metadata, video information from YouTube or Vimeo or image
+information from Flickr without using site-specific APIs since they all implement the Open Graph protocol.
 
-See [ogp.me](http://ogp.me) for information on the Open Graph protocol.
+See [ogp.me](https://ogp.me) for information on the Open Graph protocol.
 
 ## Requirements
 
-* PHP 7.4+
-* [fusonic/linq](https://github.com/fusonic/linq)
-* [symfony/css-selector](https://github.com/symfony/CssSelector)
-* [symfony/dom-crawler](https://github.com/symfony/DomCrawler)
-* [psr/http-client](https://github.com/php-fig/http-client), [psr/http-factory](https://github.com/php-fig/http-factory) and compatible implementation such as [guzzle/guzzle](https://github.com/guzzle/guzzle)
+* PHP 8.1+
+* [symfony/css-selector](https://github.com/symfony/css-selector)
+* [symfony/dom-crawler](https://github.com/symfony/dom-crawler)
+* [psr/http-client](https://github.com/php-fig/http-client)
+* [psr/http-factory](https://github.com/php-fig/http-factory)
+* and compatible implementation such as [symfony/http-client](https://github.com/symfony/http-client)
 
 ## Installation
 
 The most flexible installation method is using Composer:
 
-``` bash
+```bash
 composer require fusonic/opengraph
 ```
 
-Install composer and run install command:
-``` bash
+Install Composer and run the `install` command:
+```bash
 curl -s http://getcomposer.org/installer | php
 php composer.phar install
 ``` 
 
-Once installed, include vendor/autoload.php in your script.
+Once installed, include `vendor/autoload.php` in your script.
 
 ``` php
-require "vendor/autoload.php";
+require 'vendor/autoload.php';
 ```
 
 ## Usage
 
 ### Retrieve Open Graph data from a URL
 
-``` php
+```php
+<?php
+
 use Fusonic\OpenGraph\Consumer;
 
 $consumer = new Consumer($httpClient, $httpRequestFactory);
-$object = $consumer->loadUrl("http://www.youtube.com/watch?v=P422jZg50X4");
+$object = $consumer->loadUrl('https://www.youtube.com/watch?v=P422jZg50X4');
 
 // Basic information of the object
 echo "Title: " . $object->title;                 // Getting started with Facebook Open Graph
 echo "Site name: " . $object->siteName;          // YouTube
 echo "Description: " . $object->description;     // Originally recorded at the Facebook World ...
-echo "Canonical URL: " . $object->url;           // http://www.youtube.com/watch?v=P422jZg50X4
+echo "Canonical URL: " . $object->url;           // https://www.youtube.com/watch?v=P422jZg50X4
 
 // Images
 $image = $object->images[0];
@@ -63,7 +68,7 @@ echo "Image[0] width: " . $image->width;         // null (May return width in pi
 
 // Videos
 $video = $object->videos[0];
-echo "Video URL: " . $video->url;                // http://www.youtube.com/v/P422jZg50X4?version=3&autohide=1
+echo "Video URL: " . $video->url;                // https://www.youtube.com/v/P422jZg50X4?version=3&autohide=1
 echo "Video height: " . $video->height;          // 1080
 echo "Video width: " . $video->width;            // 1920
 echo "Video type: " . $video->type;              // application/x-shockwave-flash
@@ -73,7 +78,9 @@ _There are some more properties but these are the basic and most commonly used o
 
 ### Publish own Open Graph data
 
-``` php
+```php
+<?php
+
 use Fusonic\OpenGraph\Elements\Image;
 use Fusonic\OpenGraph\Elements\Video;
 use Fusonic\OpenGraph\Publisher;
@@ -86,14 +93,14 @@ $object = new Website();
 $object->title = "Getting started with Facebook Open Graph";
 $object->siteName = "YouTube";
 $object->description = "Originally recorded at the Facebook World ..."
-$object->url = "http://www.youtube.com/watch?v=P422jZg50X4";
+$object->url = "https://www.youtube.com/watch?v=P422jZg50X4";
 
 // Images
 $image = new Image("https://i1.ytimg.com/vi/P422jZg50X4/maxresdefault.jpg");
 $object->images[] = $image;
 
 // Videos
-$video = new Video("http://www.youtube.com/v/P422jZg50X4?version=3&autohide=1");
+$video = new Video("https://www.youtube.com/v/P422jZg50X4?version=3&autohide=1");
 $video->height = 1080;
 $video->width = 1920;
 $video->type = "application/x-shockwave-flash";
@@ -125,18 +132,20 @@ _HTML code is formatted just for displaying purposes. You may choose between HTM
 
 ## Running tests
 
-You can run the test suite by running `phpunit` from the command line.
+You can run the test suite by running `composer test` from the command line.
 
 ## FAQ
 
 **I don't get any information from a webpage, but Facebook shows information for the same URL. What do I do wrong?**
 
-It seems that some pages (like Twitter) only publish OpenGraph information if Facebook's user agent string `facebookexternalhit/1.1` is used (see #28). So you should configure your PSR-18 client to use this user agent string:
+It seems that some pages (like Twitter/X) only publish Open Graph information if Facebook's user agent string
+`facebookexternalhit/1.1` is used (see [#28](https://github.com/fusonic/opengraph/issues/28)). So you should configure
+your PSR-18 client to use this user agent string:
 
 ```php
-$client = new Psr18Client(new NativeHttpClient([ "headers" => [ "User-Agent" => "facebookexternalhit/1.1" ] ]));
+$client = new Psr18Client(new NativeHttpClient(['headers' => ['User-Agent' => 'facebookexternalhit/1.1']]));
 ```
 
 ## License
 
-This library is licensed under the MIT license.
+fusonic/opengraph is licensed under the MIT license. See [LICENSE](LICENSE) for more information.
diff --git a/UPGRADE-3.0.md b/UPGRADE-3.0.md
new file mode 100644
index 0000000..8bb9fef
--- /dev/null
+++ b/UPGRADE-3.0.md
@@ -0,0 +1,5 @@
+# UPGRADE FROM 2.2 TO 3.0
+
+## Requirements
+- Bumped the required PHP version from `^7.4 || ^8.0` to `^8.1`
+- Bumped the compatible Symfony version from `^3.0 || ^4.0 || ^5.0 || ^6.0` to `^5.4 || ^6.4 || ^7.1`
diff --git a/composer.json b/composer.json
index b74deba..b5e19e1 100644
--- a/composer.json
+++ b/composer.json
@@ -1,9 +1,11 @@
 {
     "name": "fusonic/opengraph",
     "description": "PHP library for consuming and publishing Open Graph resources.",
-    "keywords": ["opengraph"],
+    "keywords": [
+        "opengraph"
+    ],
     "type": "library",
-    "homepage": "https://github.com/fusonic/fusonic-opengraph",
+    "homepage": "https://github.com/fusonic/opengraph",
     "license": "MIT",
     "authors": [
         {
@@ -22,20 +24,34 @@
         }
     },
     "require": {
-        "php": "^7.4|^8.0",
+        "php": "^8.1",
         "ext-dom": "*",
-        "symfony/dom-crawler": "^3.0|^4.0|^5.0|^6.0",
-        "symfony/css-selector": "^3.0|^4.0|^5.0|^6.0",
+        "symfony/css-selector": "^5.4 || ^6.4 || ^7.1",
+        "symfony/dom-crawler": "^5.4 || ^6.4 || ^7.1",
         "psr/http-client": "^1.0",
         "psr/http-factory": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.0",
-        "symfony/http-client": "^6.0",
-        "nyholm/psr7": "^1.2"
+        "friendsofphp/php-cs-fixer": "^3.65",
+        "nyholm/psr7": "^1.8",
+        "phpstan/phpstan": "^2.0",
+        "phpstan/phpstan-deprecation-rules": "^2.0",
+        "phpstan/phpstan-phpunit": "^2.0",
+        "phpstan/phpstan-strict-rules": "^2.0",
+        "phpunit/phpunit": "^10.5 || ^11.4",
+        "symfony/http-client": "^5.4 || ^6.4 || ^7.1"
     },
     "suggest": {
-        "symfony/http-client": "^5.0",
-        "nyholm/psr7": "^1.2"
+        "symfony/http-client": "^5.4 || ^6.4 || ^7.1",
+        "nyholm/psr7": "^1.8"
+    },
+    "scripts": {
+        "phpcs:check": "XDEBUG_MODE=off vendor/bin/php-cs-fixer check -v --diff",
+        "phpcs:fix": "XDEBUG_MODE=off vendor/bin/php-cs-fixer fix -v",
+        "phpstan": "XDEBUG_MODE=off php -d memory_limit=2048M vendor/bin/phpstan analyse",
+        "test": "XDEBUG_MODE=off vendor/bin/phpunit --testdox"
+    },
+    "config": {
+        "sort-packages": true
     }
 }
diff --git a/examples/consume_website.php b/examples/consume_website.php
index 275cbfb..d46ce27 100644
--- a/examples/consume_website.php
+++ b/examples/consume_website.php
@@ -1,18 +1,25 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 use Symfony\Component\HttpClient\NativeHttpClient;
 use Symfony\Component\HttpClient\Psr18Client;
 
-require __DIR__ . "/../vendor/autoload.php";
+require __DIR__.'/../vendor/autoload.php';
 
 // Initialize new Psr\HttpClient implementation. This example uses Symfony's implementation from the symfony/http-client
-// package but you can use any implementation provided by your framework of choice.
-$client = new Psr18Client(new NativeHttpClient([ "headers" => [ "User-Agent" => "facebookexternalhit/1.1" ] ]));
+// package, but you can use any implementation provided by your framework of choice.
+$client = new Psr18Client(new NativeHttpClient(['headers' => ['User-Agent' => 'facebookexternalhit/1.1']]));
 
 // Create a new crawler
 $crawler = new Fusonic\OpenGraph\Consumer($client, $client);
 
 // Crawl the desired URL and retrieve a Fusonic\OpenGraph\Object in response
-$object = $crawler->loadUrl("https://github.com");
+$object = $crawler->loadUrl('https://github.com');
 
 var_dump($object);
diff --git a/examples/publish_website.php b/examples/publish_website.php
index b419765..71d9653 100644
--- a/examples/publish_website.php
+++ b/examples/publish_website.php
@@ -1,43 +1,51 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 use Fusonic\OpenGraph\Elements\Audio;
 use Fusonic\OpenGraph\Elements\Image;
 use Fusonic\OpenGraph\Elements\Video;
 use Fusonic\OpenGraph\Objects\Website;
 use Fusonic\OpenGraph\Publisher;
 
-require __DIR__ . "/../vendor/autoload.php";
+require __DIR__.'/../vendor/autoload.php';
 
 // Construct a new Open Graph object
 $website = new Website();
 
 // Set some basic properties
-$website->url = "http://www.fusonic.net";
-$website->title = "Fusonic - Intranet & Mobile Applications from Austria";
-$website->description = "Creators of the awesome fusonic-opengraph library.";
-$website->siteName = "Fusonic";
-$website->locale = "en_GB";
+$website->url = 'https://www.fusonic.net';
+$website->title = 'Fusonic - Intranet & Mobile Applications from Austria';
+$website->description = 'Creators of the awesome fusonic-opengraph library.';
+$website->siteName = 'Fusonic';
+$website->locale = 'en_GB';
 
 // Attach an image
-$image = new Image("http://www.fusonic.net/en/assets/images/logo.png");
+$image = new Image('https://www.fusonic.net/en/assets/images/logo.png');
 $image->width = 140;
 $image->height = 41;
-$image->type = "image/png";
+$image->type = 'image/png';
 $website->images[] = $image;
 
 // Attach a video
-$video = new Video("http://www.fusonic.net/en/we-dont-have-no-video.mp4");
+$video = new Video('https://www.fusonic.net/en/we-dont-have-no-video.mp4');
 $video->width = 1920;
 $video->height = 1080;
-$video->type = "video/mp4";
+$video->type = 'video/mp4';
 $website->videos[] = $video;
 
 // Attach an audio
-$audio = new Audio("http://www.fusonic.net/en/we-dont-have-no-audio.mp3");
-$audio->type = "audio/mp3";
+$audio = new Audio('https://www.fusonic.net/en/we-dont-have-no-audio.mp3');
+$audio->type = 'audio/mp3';
 $website->audios[] = $audio;
 
 // Create Publisher object and echo HTML code
 $publisher = new Publisher();
 $publisher->doctype = Publisher::DOCTYPE_HTML5;
+
 echo $publisher->generateHtml($website);
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..558a859
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,11 @@
+parameters:
+    level: 8
+    paths:
+        - src
+        - tests
+
+includes:
+    - vendor/phpstan/phpstan-deprecation-rules/rules.neon
+    - vendor/phpstan/phpstan-phpunit/extension.neon
+    - vendor/phpstan/phpstan-phpunit/rules.neon
+    - vendor/phpstan/phpstan-strict-rules/rules.neon
diff --git a/phpunit.xml b/phpunit.xml
deleted file mode 100644
index 0d9aeef..0000000
--- a/phpunit.xml
+++ /dev/null
@@ -1,12 +0,0 @@
-<phpunit bootstrap="vendor/autoload.php">
-    <testsuites>
-        <testsuite name="OpenGraph">
-            <directory>tests</directory>
-        </testsuite>
-    </testsuites>
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">src</directory>
-        </whitelist>
-    </filter>
-</phpunit>
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
new file mode 100644
index 0000000..f6aa547
--- /dev/null
+++ b/phpunit.xml.dist
@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         cacheDirectory=".phpunit.cache"
+         executionOrder="depends,defects"
+         colors="true"
+         beStrictAboutCoverageMetadata="true"
+         beStrictAboutOutputDuringTests="true"
+         displayDetailsOnTestsThatTriggerDeprecations="true"
+         displayDetailsOnTestsThatTriggerNotices="true"
+         displayDetailsOnTestsThatTriggerWarnings="true"
+         displayDetailsOnTestsThatTriggerErrors="true"
+         failOnRisky="true"
+         failOnNotice="true"
+         failOnWarning="true">
+    <php>
+        <ini name="display_errors" value="1"/>
+        <ini name="error_reporting" value="-1"/>
+        <ini name="memory_limit" value="512M"/>
+    </php>
+
+    <testsuites>
+        <testsuite name="Fusonic OpenGraph">
+            <directory>./tests/</directory>
+        </testsuite>
+    </testsuites>
+
+    <source restrictNotices="true"
+            ignoreSuppressionOfNotices="true"
+            ignoreSuppressionOfPhpNotices="true"
+            restrictWarnings="true"
+            ignoreSuppressionOfWarnings="true"
+            ignoreSuppressionOfPhpWarnings="true"
+            ignoreSuppressionOfErrors="true">
+            <!-- Add to source tag once PHP 8.1 support is dropped and only PHPUnit 11 is used -->
+            <!-- ignoreIndirectDeprecations="true" -->
+            <!-- ignoreSuppressionOfDeprecations="true" -->
+            <!-- ignoreSuppressionOfPhpDeprecations="true" -->
+        <include>
+            <directory>src</directory>
+        </include>
+    </source>
+</phpunit>
diff --git a/src/Consumer.php b/src/Consumer.php
index 74aec6a..7dc884a 100644
--- a/src/Consumer.php
+++ b/src/Consumer.php
@@ -1,23 +1,26 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph;
 
 use Fusonic\OpenGraph\Objects\ObjectBase;
 use Fusonic\OpenGraph\Objects\Website;
-use LogicException;
 use Psr\Http\Client\ClientExceptionInterface;
 use Psr\Http\Client\ClientInterface;
 use Psr\Http\Message\RequestFactoryInterface;
 use Symfony\Component\DomCrawler\Crawler;
 
 /**
- * Consumer that extracts Open Graph data from either a URL or a HTML string.
+ * Consumer that extracts Open Graph data from either a URL or an HTML string.
  */
 class Consumer
 {
-    private ?ClientInterface $client;
-    private ?RequestFactoryInterface $requestFactory;
-
     /**
      * When enabled, crawler will read content of title and meta description if no
      * Open Graph data is provided by target page.
@@ -31,33 +34,31 @@ class Consumer
     public bool $debug = false;
 
     /**
-     * @param ClientInterface|null         $client         A PSR-18 ClientInterface implementation.
-     * @param RequestFactoryInterface|null $requestFactory A PSR-17 RequestFactoryInterface implementation.
+     * @param ClientInterface|null         $client         a PSR-18 ClientInterface implementation
+     * @param RequestFactoryInterface|null $requestFactory a PSR-17 RequestFactoryInterface implementation
      */
-    public function __construct(?ClientInterface $client = null, ?RequestFactoryInterface $requestFactory = null)
-    {
-        $this->client = $client;
-        $this->requestFactory = $requestFactory;
+    public function __construct(
+        private ?ClientInterface $client = null,
+        private ?RequestFactoryInterface $requestFactory = null,
+    ) {
     }
 
     /**
      * Fetches HTML content from the given URL and then crawls it for Open Graph data.
      *
-     * @param string $url URL to be crawled.
-     *
-     * @return ObjectBase
+     * @param string $url URL to be crawled
      *
      * @throws ClientExceptionInterface
      */
     public function loadUrl(string $url): ObjectBase
     {
-        if ($this->client === null) {
-            throw new LogicException(
-                "To use loadUrl() you must provide \$client and \$requestFactory when instantiating the consumer."
+        if (null === $this->client || null === $this->requestFactory) {
+            throw new \LogicException(
+                'To use loadUrl() you must provide $client and $requestFactory when instantiating the consumer.'
             );
         }
 
-        $request = $this->requestFactory->createRequest("GET", $url);
+        $request = $this->requestFactory->createRequest('GET', $url);
         $response = $this->client->sendRequest($request);
 
         return $this->loadHtml($response->getBody()->getContents(), $url);
@@ -66,18 +67,16 @@ public function loadUrl(string $url): ObjectBase
     /**
      * Crawls the given HTML string for OpenGraph data.
      *
-     * @param string $html        HTML string, usually whole content of crawled web resource.
-     * @param string $fallbackUrl URL to use when fallback mode is enabled.
-     *
-     * @return  ObjectBase
+     * @param string      $html        HTML string, usually whole content of crawled web resource
+     * @param string|null $fallbackUrl URL to use when fallback mode is enabled
      */
-    public function loadHtml(string $html, string $fallbackUrl = null): ObjectBase
+    public function loadHtml(string $html, ?string $fallbackUrl = null): ObjectBase
     {
         // Extract all data that can be found
         $page = $this->extractOpenGraphData($html);
 
         // Use the user's URL as fallback
-        if ($this->useFallbackMode && $page->url === null) {
+        if ($this->useFallbackMode && null === $page->url) {
             $page->url = $fallbackUrl;
         }
 
@@ -87,26 +86,27 @@ public function loadHtml(string $html, string $fallbackUrl = null): ObjectBase
 
     private function extractOpenGraphData(string $content): ObjectBase
     {
-        $crawler = new Crawler;
-        $crawler->addHTMLContent($content, 'UTF-8');
+        $crawler = new Crawler();
+        $crawler->addHtmlContent(content: $content);
 
         $properties = [];
-        foreach(['name', 'property'] as $t)
-        {
+        foreach (['name', 'property'] as $t) {
             // Get all meta-tags starting with "og:"
             $ogMetaTags = $crawler->filter("meta[{$t}^='og:']");
 
             // Create clean property array
             $props = [];
+
+            /** @var \DOMElement $tag */
             foreach ($ogMetaTags as $tag) {
                 $name = strtolower(trim($tag->getAttribute($t)));
-                $value = trim($tag->getAttribute("content"));
+                $value = trim($tag->getAttribute('content'));
                 $props[] = new Property($name, $value);
             }
 
             $properties = array_merge($properties, $props);
         }
-            
+
         // Create new object
         $object = new Website();
 
@@ -114,26 +114,26 @@ private function extractOpenGraphData(string $content): ObjectBase
         $object->assignProperties($properties, $this->debug);
 
         // Fallback for url
-        if ($this->useFallbackMode && !$object->url) {
+        if ($this->useFallbackMode && null === $object->url) {
             $urlElement = $crawler->filter("link[rel='canonical']")->first();
             if ($urlElement->count() > 0) {
-                $object->url = trim($urlElement->attr("href"));
+                $object->url = trim($urlElement->attr('href') ?? '');
             }
         }
 
         // Fallback for title
-        if ($this->useFallbackMode && !$object->title) {
-            $titleElement = $crawler->filter("title")->first();
+        if ($this->useFallbackMode && null === $object->title) {
+            $titleElement = $crawler->filter('title')->first();
             if ($titleElement->count() > 0) {
                 $object->title = trim($titleElement->text());
             }
         }
 
         // Fallback for description
-        if ($this->useFallbackMode && !$object->description) {
+        if ($this->useFallbackMode && null === $object->description) {
             $descriptionElement = $crawler->filter("meta[property='description']")->first();
             if ($descriptionElement->count() > 0) {
-                $object->description = trim($descriptionElement->attr("content"));
+                $object->description = trim($descriptionElement->attr('content') ?? '');
             }
         }
 
diff --git a/src/Elements/Audio.php b/src/Elements/Audio.php
index 20df532..394348c 100644
--- a/src/Elements/Audio.php
+++ b/src/Elements/Audio.php
@@ -1,5 +1,12 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Elements;
 
 use Fusonic\OpenGraph\Property;
@@ -11,54 +18,46 @@ class Audio extends ElementBase
 {
     /**
      * The URL of an audio resource associated with the object.
-     *
-     * @var string
      */
-    public $url;
+    public ?string $url = null;
 
     /**
      * An alternate URL to use if an audio resource requires HTTPS.
-     *
-     * @var string
      */
-    public $secureUrl;
+    public ?string $secureUrl = null;
 
     /**
      * The MIME type of an audio resource associated with the object.
-     *
-     * @var type
      */
-    public $type;
+    public ?string $type = null;
 
     /**
-     * @param   string      $url            URL to the audio file.
+     * @param string $url URL to the audio file
      */
-    public function __construct($url)
+    public function __construct(string $url)
     {
-        parent::__construct();
-
         $this->url = $url;
     }
 
     /**
      * Gets all properties set on this element.
      *
-     * @return  array|Property[]
+     * @return Property[]
      */
-    public function getProperties()
+    public function getProperties(): array
     {
         $properties = [];
 
         // URL must precede all other properties
-        if ($this->url !== null) {
+        if (null !== $this->url) {
             $properties[] = new Property(Property::AUDIO_URL, $this->url);
         }
 
-        if ($this->secureUrl !== null) {
+        if (null !== $this->secureUrl) {
             $properties[] = new Property(Property::AUDIO_SECURE_URL, $this->secureUrl);
         }
 
-        if ($this->type !== null) {
+        if (null !== $this->type) {
             $properties[] = new Property(Property::AUDIO_TYPE, $this->type);
         }
 
diff --git a/src/Elements/ElementBase.php b/src/Elements/ElementBase.php
index dd4139d..5660064 100644
--- a/src/Elements/ElementBase.php
+++ b/src/Elements/ElementBase.php
@@ -1,20 +1,25 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Elements;
 
+use Fusonic\OpenGraph\Property;
+
 /**
- * Abstract base class for all OpenGraph elements (e.g. images, videos etc.)
+ * Abstract base class for all OpenGraph elements (e.g. images, videos etc.).
  */
 abstract class ElementBase
 {
-    protected function __construct()
-    {
-    }
-
     /**
      * Gets all properties set on this element.
      *
-     * @return  array|Property[]
+     * @return Property[]
      */
-    abstract public function getProperties();
+    abstract public function getProperties(): array;
 }
diff --git a/src/Elements/Image.php b/src/Elements/Image.php
index 831a0c4..9087336 100644
--- a/src/Elements/Image.php
+++ b/src/Elements/Image.php
@@ -1,5 +1,12 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Elements;
 
 use Fusonic\OpenGraph\Property;
@@ -11,87 +18,73 @@ class Image extends ElementBase
 {
     /**
      * The URL of an image resource associated with the object.
-     *
-     * @var string
      */
-    public $url;
+    public ?string $url = null;
 
     /**
      * An alternate URL to use if an image resource requires HTTPS.
-     *
-     * @var string
      */
-    public $secureUrl;
+    public ?string $secureUrl = null;
 
     /**
      * The MIME type of an image resource.
-     *
-     * @var type
      */
-    public $type;
+    public ?string $type = null;
 
     /**
      * The width of an image resource in pixels.
-     *
-     * @var int
      */
-    public $width;
+    public ?int $width = null;
 
     /**
      * The height of an image resource in pixels.
-     *
-     * @var int
      */
-    public $height;
+    public ?int $height = null;
 
     /**
      * Whether the image is user-generated or not.
-     *
-     * @var bool
      */
-    public $userGenerated;
+    public ?bool $userGenerated = null;
 
     /**
-     * @param   string      $url            URL to the image file.
+     * @param string $url URL to the image file
      */
-    public function __construct($url)
+    public function __construct(string $url)
     {
-        parent::__construct();
-
         $this->url = $url;
     }
 
     /**
      * Gets all properties set on this element.
      *
-     * @return  array|Property[]
+     * @return Property[]
      */
-    public function getProperties()
+    public function getProperties(): array
     {
         $properties = [];
 
         // URL must precede all other properties
-        if ($this->url !== null) {
+        if (null !== $this->url) {
             $properties[] = new Property(Property::IMAGE_URL, $this->url);
         }
 
-        if ($this->height !== null) {
+        if (null !== $this->height) {
             $properties[] = new Property(Property::IMAGE_HEIGHT, $this->height);
         }
 
-        if ($this->secureUrl !== null) {
+        if (null !== $this->secureUrl) {
             $properties[] = new Property(Property::IMAGE_SECURE_URL, $this->secureUrl);
         }
 
-        if ($this->type !== null) {
+        if (null !== $this->type) {
             $properties[] = new Property(Property::IMAGE_TYPE, $this->type);
         }
 
-        if ($this->width !== null) {
+        if (null !== $this->width) {
             $properties[] = new Property(Property::IMAGE_WIDTH, $this->width);
         }
 
-        if ($this->userGenerated !== null) {
+        if (null !== $this->userGenerated) {
             $properties[] = new Property(Property::IMAGE_USER_GENERATED, $this->userGenerated);
         }
 
diff --git a/src/Elements/Video.php b/src/Elements/Video.php
index ff5a330..c5062fe 100644
--- a/src/Elements/Video.php
+++ b/src/Elements/Video.php
@@ -1,5 +1,12 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Elements;
 
 use Fusonic\OpenGraph\Property;
@@ -11,76 +18,64 @@ class Video extends ElementBase
 {
     /**
      * The URL of a video resource associated with the object.
-     *
-     * @var string
      */
-    public $url;
+    public ?string $url = null;
 
     /**
      * An alternate URL to use if a video resource requires HTTPS.
-     *
-     * @var string
      */
-    public $secureUrl;
+    public ?string $secureUrl = null;
 
     /**
      * The MIME type of a video resource associated with the object.
-     *
-     * @var type
      */
-    public $type;
+    public ?string $type = null;
 
     /**
      * The width of a video resource associated with the object in pixels.
-     *
-     * @var int
      */
-    public $width;
+    public ?int $width = null;
 
     /**
      * The height of a video resource associated with the object in pixels.
-     *
-     * @var int
      */
-    public $height;
+    public ?int $height = null;
 
     /**
-     * @param   string      $url            URL to the video.
+     * @param string $url URL to the video
      */
-    public function __construct($url)
+    public function __construct(string $url)
     {
-        parent::__construct();
-
         $this->url = $url;
     }
 
     /**
      * Gets all properties set on this element.
      *
-     * @return  array|Property[]
+     * @return Property[]
      */
-    public function getProperties()
+    public function getProperties(): array
     {
         $properties = [];
 
         // URL must precede all other properties
-        if ($this->url !== null) {
+        if (null !== $this->url) {
             $properties[] = new Property(Property::VIDEO_URL, $this->url);
         }
 
-        if ($this->height !== null) {
+        if (null !== $this->height) {
             $properties[] = new Property(Property::VIDEO_HEIGHT, $this->height);
         }
 
-        if ($this->secureUrl !== null) {
+        if (null !== $this->secureUrl) {
             $properties[] = new Property(Property::VIDEO_SECURE_URL, $this->secureUrl);
         }
 
-        if ($this->type !== null) {
+        if (null !== $this->type) {
             $properties[] = new Property(Property::VIDEO_TYPE, $this->type);
         }
 
-        if ($this->width !== null) {
+        if (null !== $this->width) {
             $properties[] = new Property(Property::VIDEO_WIDTH, $this->width);
         }
 
diff --git a/src/Objects/ObjectBase.php b/src/Objects/ObjectBase.php
index 33b9976..40e3bf9 100644
--- a/src/Objects/ObjectBase.php
+++ b/src/Objects/ObjectBase.php
@@ -1,16 +1,21 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Objects;
 
-use DateTimeImmutable;
 use Fusonic\OpenGraph\Elements\Audio;
 use Fusonic\OpenGraph\Elements\Image;
 use Fusonic\OpenGraph\Elements\Video;
 use Fusonic\OpenGraph\Property;
-use UnexpectedValueException;
 
 /**
- * Abstract base class for all Open Graph objects (website, video, ...)
+ * Abstract base class for all Open Graph objects (website, video, ...).
  */
 abstract class ObjectBase
 {
@@ -79,7 +84,7 @@ abstract class ObjectBase
     /**
      * The time when the object was last updated.
      */
-    public ?DateTimeImmutable $updatedTime = null;
+    public ?\DateTimeImmutable $updatedTime = null;
 
     /**
      * The canonical URL of the object, used as its ID in the graph.
@@ -93,36 +98,32 @@ abstract class ObjectBase
      */
     public array $videos = [];
 
-    public function __construct()
-    {
-    }
-
     /**
      * Assigns all properties given to the this Object instance.
      *
-     * @param   array|Property[]    $properties     Array of all properties to assign.
-     * @param   bool                $debug          Throw exceptions when parsing or not.
+     * @param array|Property[] $properties array of all properties to assign
+     * @param bool             $debug      throw exceptions when parsing or not
      *
-     * @throws  UnexpectedValueException
+     * @throws \UnexpectedValueException
      */
-    public function assignProperties(array $properties, $debug = false): void
+    public function assignProperties(array $properties, bool $debug = false): void
     {
         foreach ($properties as $property) {
             $name = $property->key;
             $value = $property->value;
 
-            switch($name) {
+            switch ($name) {
                 case Property::AUDIO:
                 case Property::AUDIO_URL:
                     $this->audios[] = new Audio($value);
                     break;
                 case Property::AUDIO_SECURE_URL:
                 case Property::AUDIO_TYPE:
-                    if (count($this->audios) > 0) {
-                        $this->handleAudioAttribute($this->audios[count($this->audios) - 1], $name, $value);
+                    if (\count($this->audios) > 0) {
+                        $this->handleAudioAttribute($this->audios[\count($this->audios) - 1], $name, $value);
                     } elseif ($debug) {
-                        throw new UnexpectedValueException(
-                            sprintf(
+                        throw new \UnexpectedValueException(
+                            \sprintf(
                                 "Found '%s' property but no audio was found before.",
                                 $name
                             )
@@ -130,12 +131,12 @@ public function assignProperties(array $properties, $debug = false): void
                     }
                     break;
                 case Property::DESCRIPTION:
-                    if ($this->description === null) {
+                    if (null === $this->description) {
                         $this->description = $value;
                     }
                     break;
                 case Property::DETERMINER:
-                    if ($this->determiner === null) {
+                    if (null === $this->determiner) {
                         $this->determiner = $value;
                     }
                     break;
@@ -148,11 +149,11 @@ public function assignProperties(array $properties, $debug = false): void
                 case Property::IMAGE_TYPE:
                 case Property::IMAGE_WIDTH:
                 case Property::IMAGE_USER_GENERATED:
-                    if (count($this->images) > 0) {
-                        $this->handleImageAttribute($this->images[count($this->images) - 1], $name, $value);
+                    if (\count($this->images) > 0) {
+                        $this->handleImageAttribute($this->images[\count($this->images) - 1], $name, $value);
                     } elseif ($debug) {
-                        throw new UnexpectedValueException(
-                            sprintf(
+                        throw new \UnexpectedValueException(
+                            \sprintf(
                                 "Found '%s' property but no image was found before.",
                                 $name
                             )
@@ -160,7 +161,7 @@ public function assignProperties(array $properties, $debug = false): void
                     }
                     break;
                 case Property::LOCALE:
-                    if ($this->locale === null) {
+                    if (null === $this->locale) {
                         $this->locale = $value;
                     }
                     break;
@@ -174,22 +175,22 @@ public function assignProperties(array $properties, $debug = false): void
                     $this->seeAlso[] = $value;
                     break;
                 case Property::SITE_NAME:
-                    if ($this->siteName === null) {
+                    if (null === $this->siteName) {
                         $this->siteName = $value;
                     }
                     break;
                 case Property::TITLE:
-                    if ($this->title === null) {
+                    if (null === $this->title) {
                         $this->title = $value;
                     }
                     break;
                 case Property::UPDATED_TIME:
-                    if ($this->updatedTime === null) {
+                    if (null === $this->updatedTime) {
                         $this->updatedTime = $this->convertToDateTime($value);
                     }
                     break;
                 case Property::URL:
-                    if ($this->url === null) {
+                    if (null === $this->url) {
                         $this->url = $value;
                     }
                     break;
@@ -201,10 +202,10 @@ public function assignProperties(array $properties, $debug = false): void
                 case Property::VIDEO_SECURE_URL:
                 case Property::VIDEO_TYPE:
                 case Property::VIDEO_WIDTH:
-                    if (count($this->videos) > 0) {
-                        $this->handleVideoAttribute($this->videos[count($this->videos) - 1], $name, $value);
+                    if (\count($this->videos) > 0) {
+                        $this->handleVideoAttribute($this->videos[\count($this->videos) - 1], $name, $value);
                     } elseif ($debug) {
-                        throw new UnexpectedValueException(sprintf(
+                        throw new \UnexpectedValueException(\sprintf(
                             "Found '%s' property but no video was found before.",
                             $name
                         ));
@@ -215,13 +216,12 @@ public function assignProperties(array $properties, $debug = false): void
 
     private function handleImageAttribute(Image $element, string $name, string $value): void
     {
-        switch($name)
-        {
+        switch ($name) {
             case Property::IMAGE_HEIGHT:
-                $element->height = (int)$value;
+                $element->height = (int) $value;
                 break;
             case Property::IMAGE_WIDTH:
-                $element->width = (int)$value;
+                $element->width = (int) $value;
                 break;
             case Property::IMAGE_TYPE:
                 $element->type = $value;
@@ -237,13 +237,12 @@ private function handleImageAttribute(Image $element, string $name, string $valu
 
     private function handleVideoAttribute(Video $element, string $name, string $value): void
     {
-        switch($name)
-        {
+        switch ($name) {
             case Property::VIDEO_HEIGHT:
-                $element->height = (int)$value;
+                $element->height = (int) $value;
                 break;
             case Property::VIDEO_WIDTH:
-                $element->width = (int)$value;
+                $element->width = (int) $value;
                 break;
             case Property::VIDEO_TYPE:
                 $element->type = $value;
@@ -256,8 +255,7 @@ private function handleVideoAttribute(Video $element, string $name, string $valu
 
     private function handleAudioAttribute(Audio $element, string $name, string $value): void
     {
-        switch($name)
-        {
+        switch ($name) {
             case Property::AUDIO_TYPE:
                 $element->type = $value;
                 break;
@@ -267,10 +265,10 @@ private function handleAudioAttribute(Audio $element, string $name, string $valu
         }
     }
 
-    protected function convertToDateTime(string $value): ?DateTimeImmutable
+    protected function convertToDateTime(string $value): ?\DateTimeImmutable
     {
         try {
-            return new DateTimeImmutable($value);
+            return new \DateTimeImmutable($value);
         } catch (\Exception $e) {
             return null;
         }
@@ -278,10 +276,9 @@ protected function convertToDateTime(string $value): ?DateTimeImmutable
 
     protected function convertToBoolean(string $value): bool
     {
-        switch(strtolower($value))
-        {
-            case "1":
-            case "true":
+        switch (strtolower($value)) {
+            case '1':
+            case 'true':
                 return true;
             default:
                 return false;
@@ -291,7 +288,7 @@ protected function convertToBoolean(string $value): bool
     /**
      * Gets all properties set on this object.
      *
-     * @return  Property[]
+     * @return Property[]
      */
     public function getProperties(): array
     {
@@ -300,16 +297,16 @@ public function getProperties(): array
         foreach ($this->audios as $audio) {
             $properties = array_merge($properties, $audio->getProperties());
         }
-        
-        if ($this->title !== null) {
+
+        if (null !== $this->title) {
             $properties[] = new Property(Property::TITLE, $this->title);
         }
 
-        if ($this->description !== null) {
+        if (null !== $this->description) {
             $properties[] = new Property(Property::DESCRIPTION, $this->description);
         }
 
-        if ($this->determiner !== null) {
+        if (null !== $this->determiner) {
             $properties[] = new Property(Property::DETERMINER, $this->determiner);
         }
 
@@ -317,7 +314,7 @@ public function getProperties(): array
             $properties = array_merge($properties, $image->getProperties());
         }
 
-        if ($this->locale !== null) {
+        if (null !== $this->locale) {
             $properties[] = new Property(Property::LOCALE, $this->locale);
         }
 
@@ -325,27 +322,27 @@ public function getProperties(): array
             $properties[] = new Property(Property::LOCALE_ALTERNATE, $locale);
         }
 
-        if ($this->richAttachment !== null) {
-            $properties[] = new Property(Property::RICH_ATTACHMENT, (int)$this->richAttachment);
+        if (null !== $this->richAttachment) {
+            $properties[] = new Property(Property::RICH_ATTACHMENT, (int) $this->richAttachment);
         }
 
         foreach ($this->seeAlso as $seeAlso) {
             $properties[] = new Property(Property::SEE_ALSO, $seeAlso);
         }
 
-        if ($this->siteName !== null) {
+        if (null !== $this->siteName) {
             $properties[] = new Property(Property::SITE_NAME, $this->siteName);
         }
 
-        if ($this->type !== null) {
+        if (null !== $this->type) {
             $properties[] = new Property(Property::TYPE, $this->type);
         }
 
-        if ($this->updatedTime !== null) {
-            $properties[] = new Property(Property::UPDATED_TIME, $this->updatedTime->format("c"));
+        if (null !== $this->updatedTime) {
+            $properties[] = new Property(Property::UPDATED_TIME, $this->updatedTime->format('c'));
         }
 
-        if ($this->url !== null) {
+        if (null !== $this->url) {
             $properties[] = new Property(Property::URL, $this->url);
         }
 
diff --git a/src/Objects/Website.php b/src/Objects/Website.php
index f66428c..a973c77 100644
--- a/src/Objects/Website.php
+++ b/src/Objects/Website.php
@@ -1,5 +1,12 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Objects;
 
 /**
@@ -10,12 +17,10 @@
  */
 class Website extends ObjectBase
 {
-    const TYPE = "website";
+    public const TYPE = 'website';
 
     public function __construct()
     {
-        parent::__construct();
-
         $this->type = self::TYPE;
     }
 }
diff --git a/src/Property.php b/src/Property.php
index e94593b..00fe7be 100644
--- a/src/Property.php
+++ b/src/Property.php
@@ -1,5 +1,12 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph;
 
 /**
@@ -7,48 +14,45 @@
  */
 class Property
 {
-    const AUDIO = "og:audio";
-    const AUDIO_SECURE_URL = "og:audio:secure_url";
-    const AUDIO_TYPE = "og:audio:type";
-    const AUDIO_URL = "og:audio:url";
-    const DESCRIPTION = "og:description";
-    const DETERMINER = "og:determiner";
-    const IMAGE = "og:image";
-    const IMAGE_HEIGHT = "og:image:height";
-    const IMAGE_SECURE_URL = "og:image:secure_url";
-    const IMAGE_TYPE = "og:image:type";
-    const IMAGE_URL = "og:image:url";
-    const IMAGE_WIDTH = "og:image:width";
-    const IMAGE_USER_GENERATED = "og:image:user_generated";
-    const LOCALE = "og:locale";
-    const LOCALE_ALTERNATE = "og:locale:alternate";
-    const RICH_ATTACHMENT = "og:rich_attachment";
-    const SEE_ALSO = "og:see_also";
-    const SITE_NAME = "og:site_name";
-    const TITLE = "og:title";
-    const TYPE = "og:type";
-    const UPDATED_TIME = "og:updated_time";
-    const URL = "og:url";
-    const VIDEO = "og:video";
-    const VIDEO_HEIGHT = "og:video:height";
-    const VIDEO_SECURE_URL = "og:video:secure_url";
-    const VIDEO_TYPE = "og:video:type";
-    const VIDEO_URL = "og:video:url";
-    const VIDEO_WIDTH = "og:video:width";
-
-    /**
-     * Key of the property without "og:" prefix.
-     */
-    public string $key;
+    public const AUDIO = 'og:audio';
+    public const AUDIO_SECURE_URL = 'og:audio:secure_url';
+    public const AUDIO_TYPE = 'og:audio:type';
+    public const AUDIO_URL = 'og:audio:url';
+    public const DESCRIPTION = 'og:description';
+    public const DETERMINER = 'og:determiner';
+    public const IMAGE = 'og:image';
+    public const IMAGE_HEIGHT = 'og:image:height';
+    public const IMAGE_SECURE_URL = 'og:image:secure_url';
+    public const IMAGE_TYPE = 'og:image:type';
+    public const IMAGE_URL = 'og:image:url';
+    public const IMAGE_WIDTH = 'og:image:width';
+    public const IMAGE_USER_GENERATED = 'og:image:user_generated';
+    public const LOCALE = 'og:locale';
+    public const LOCALE_ALTERNATE = 'og:locale:alternate';
+    public const RICH_ATTACHMENT = 'og:rich_attachment';
+    public const SEE_ALSO = 'og:see_also';
+    public const SITE_NAME = 'og:site_name';
+    public const TITLE = 'og:title';
+    public const TYPE = 'og:type';
+    public const UPDATED_TIME = 'og:updated_time';
+    public const URL = 'og:url';
+    public const VIDEO = 'og:video';
+    public const VIDEO_HEIGHT = 'og:video:height';
+    public const VIDEO_SECURE_URL = 'og:video:secure_url';
+    public const VIDEO_TYPE = 'og:video:type';
+    public const VIDEO_URL = 'og:video:url';
+    public const VIDEO_WIDTH = 'og:video:width';
 
-    /**
-     * Value of the property.
-     */
-    public $value;
+    public function __construct(
+        /**
+         * Key of the property without "og:" prefix.
+         */
+        public string $key,
 
-    public function __construct(string $key, $value)
-    {
-        $this->key = $key;
-        $this->value = $value;
+        /**
+         * Value of the property.
+         */
+        public mixed $value,
+    ) {
     }
 }
diff --git a/src/Publisher.php b/src/Publisher.php
index 059363a..7a6eb66 100644
--- a/src/Publisher.php
+++ b/src/Publisher.php
@@ -1,18 +1,23 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph;
 
-use DateTimeInterface;
 use Fusonic\OpenGraph\Objects\ObjectBase;
-use UnexpectedValueException;
 
 /**
  * Class for generating Open Graph tags from objects.
  */
 class Publisher
 {
-    const DOCTYPE_HTML5 = 1;
-    const DOCTYPE_XHTML = 2;
+    public const DOCTYPE_HTML5 = 1;
+    public const DOCTYPE_XHTML = 2;
 
     /**
      * Defines the style in which HTML tags should be written. Use one of Publisher::DOCTYPE_HTML5 or
@@ -20,44 +25,40 @@ class Publisher
      */
     public int $doctype = self::DOCTYPE_HTML5;
 
-    public function __construct()
-    {
-    }
-
     /**
      * Generated HTML tags from the given object.
      */
     public function generateHtml(ObjectBase $object): string
     {
-        $html = "";
-        $format = "<meta property=\"%s\" content=\"%s\"" . ($this->doctype == self::DOCTYPE_XHTML ? " />" : ">");
+        $html = '';
+        $format = '<meta property="%s" content="%s"'.(self::DOCTYPE_XHTML === $this->doctype ? ' />' : '>');
 
         foreach ($object->getProperties() as $property) {
-            if ($html !== "") {
+            if ('' !== $html) {
                 $html .= "\n";
             }
 
-            if ($property->value === null) {
+            if (null === $property->value) {
                 continue;
-            } elseif ($property->value instanceof DateTimeInterface) {
-                $value = $property->value->format("c");
-            } elseif (is_object($property->value)) {
-                throw new UnexpectedValueException(
-                    sprintf(
+            } elseif ($property->value instanceof \DateTimeInterface) {
+                $value = $property->value->format('c');
+            } elseif (\is_object($property->value)) {
+                throw new \UnexpectedValueException(
+                    \sprintf(
                         "Cannot handle value of type '%s' for property '%s'.",
-                        get_class($property->value),
+                        \get_class($property->value),
                         $property->key
                     )
                 );
-            } elseif ($property->value === true) {
-                $value = "1";
-            } elseif ($property->value === false) {
-                $value = "0";
+            } elseif (true === $property->value) {
+                $value = '1';
+            } elseif (false === $property->value) {
+                $value = '0';
             } else {
-                $value = (string)$property->value;
+                $value = (string) $property->value;
             }
 
-            $html .= sprintf($format, $property->key, htmlspecialchars($value));
+            $html .= \sprintf($format, $property->key, htmlspecialchars($value));
         }
 
         return $html;
diff --git a/tests/ConsumerTest.php b/tests/ConsumerTest.php
index 4fa285c..652d124 100644
--- a/tests/ConsumerTest.php
+++ b/tests/ConsumerTest.php
@@ -1,387 +1,442 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Test;
 
 use Fusonic\OpenGraph\Consumer;
 use PHPUnit\Framework\TestCase;
 
-class ConsumerTest extends TestCase
+final class ConsumerTest extends TestCase
 {
     /**
      * Checks crawler to read basic properties.
      */
-    public function testLoadHtmlBasics()
+    public function testLoadHtmlBasics(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:description" content="Description">
-<meta property="og:determiner" content="auto">
-<meta property="og:locale" content="en_GB">
-<meta property="og:locale:alternate" content="en_US">
-<meta property="og:locale:alternate" content="de_AT">
-<meta property="og:rich_attachment" content="True">
-<meta property="og:see_also" content="https://github.com/fusonic/fusonic-linq">
-<meta property="og:see_also" content="https://github.com/fusonic/fusonic-spreadsheetexport">
-<meta property="og:site_name" content="Site name">
-<meta property="og:title" content="Title">
-<meta property="og:updated_time" content="2014-07-20T17:51:00+02:00">
-<meta property="og:url" content="https://github.com/fusonic/fusonic-opengraph">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:description" content="Description">
+                    <meta property="og:determiner" content="auto">
+                    <meta property="og:locale" content="en_GB">
+                    <meta property="og:locale:alternate" content="en_US">
+                    <meta property="og:locale:alternate" content="de_AT">
+                    <meta property="og:rich_attachment" content="True">
+                    <meta property="og:see_also" content="https://github.com/fusonic/fusonic-linq">
+                    <meta property="og:see_also" content="https://github.com/fusonic/fusonic-spreadsheetexport">
+                    <meta property="og:site_name" content="Site name">
+                    <meta property="og:title" content="Title">
+                    <meta property="og:updated_time" content="2014-07-20T17:51:00+02:00">
+                    <meta property="og:url" content="https://github.com/fusonic/fusonic-opengraph">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content, "about:blank");
-
-        $this->assertEquals("Description", $res->description);
-        $this->assertEquals("auto", $res->determiner);
-        $this->assertEquals("en_GB", $res->locale);
-        $this->assertContains("en_US", $res->localeAlternate);
-        $this->assertContains("de_AT", $res->localeAlternate);
-        $this->assertTrue($res->richAttachment);
-        $this->assertContains("https://github.com/fusonic/fusonic-linq", $res->seeAlso);
-        $this->assertContains("https://github.com/fusonic/fusonic-spreadsheetexport", $res->seeAlso);
-        $this->assertEquals("Site name", $res->siteName);
-        $this->assertEquals("Title", $res->title);
-        $this->assertTrue($res->updatedTime instanceof \DateTimeInterface);
-        $this->assertEquals("https://github.com/fusonic/fusonic-opengraph", $res->url);
+        // act
+        $result = $consumer->loadHtml($content, 'about:blank');
+
+        // assert
+        self::assertSame('Description', $result->description);
+        self::assertSame('auto', $result->determiner);
+        self::assertSame('en_GB', $result->locale);
+        self::assertContains('en_US', $result->localeAlternate);
+        self::assertContains('de_AT', $result->localeAlternate);
+        self::assertTrue($result->richAttachment);
+        self::assertContains('https://github.com/fusonic/fusonic-linq', $result->seeAlso);
+        self::assertContains('https://github.com/fusonic/fusonic-spreadsheetexport', $result->seeAlso);
+        self::assertSame('Site name', $result->siteName);
+        self::assertSame('Title', $result->title);
+        self::assertInstanceOf(\DateTimeInterface::class, $result->updatedTime);
+        self::assertSame('https://github.com/fusonic/fusonic-opengraph', $result->url);
     }
 
     /**
      * Checks crawler not to use fallback if disabled even if no OG data is provided.
      */
-    public function testLoadHtmlFallbacksOff()
+    public function testLoadHtmlFallbacksOff(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<title>Title</title>
-<meta property="description" content="Description">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <title>Title</title>
+                    <meta property="description" content="Description">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content, "about:blank");
+        // act
+        $result = $consumer->loadHtml($content, 'about:blank');
 
-        $this->assertNull($res->description);
-        $this->assertNull($res->title);
-        $this->assertNull($res->url);
+        // assert
+        self::assertNull($result->description);
+        self::assertNull($result->title);
+        self::assertNull($result->url);
     }
 
     /**
      * Checks crawler to correctly use fallback elements when activated.
      */
-    public function testLoadHtmlFallbacksOn()
+    public function testLoadHtmlFallbacksOn(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<title>Title</title>
-<meta property="description" content="Description">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <title>Title</title>
+                    <meta property="description" content="Description">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
         $consumer->useFallbackMode = true;
 
-        $res = $consumer->loadHtml($content, "about:blank");
+        // act
+        $result = $consumer->loadHtml($content, 'about:blank');
 
-        $this->assertEquals("Description", $res->description);
-        $this->assertEquals("Title", $res->title);
-        $this->assertEquals("about:blank", $res->url);
+        // assert
+        self::assertSame('Description', $result->description);
+        self::assertSame('Title', $result->title);
+        self::assertSame('about:blank', $result->url);
     }
 
     /**
      * Checks crawler to correctly use fallback elements when activated.
      */
-    public function testLoadHtmlCanonicalLinkFallbacksOn()
+    public function testLoadHtmlCanonicalLinkFallbacksOn(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<title>Title</title>
-<meta property="description" content="Description">
-<link rel="canonical" href="https://github.com/fusonic/opengraph">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <title>Title</title>
+                    <meta property="description" content="Description">
+                    <link rel="canonical" href="https://github.com/fusonic/opengraph">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
         $consumer->useFallbackMode = true;
 
-        $res = $consumer->loadHtml($content, "about:blank");
+        // act
+        $result = $consumer->loadHtml($content, 'about:blank');
 
-        $this->assertEquals("Description", $res->description);
-        $this->assertEquals("Title", $res->title);
-        $this->assertEquals("https://github.com/fusonic/opengraph", $res->url);
+        // assert
+        self::assertSame('Description', $result->description);
+        self::assertSame('Title', $result->title);
+        self::assertSame('https://github.com/fusonic/opengraph', $result->url);
     }
 
     /**
      * Checks crawler to handle arrays of elements with child-properties like described in the
      * Open Graph documentation (http://ogp.me/#array).
      */
-    public function testLoadHtmlArrayHandling()
+    public function testLoadHtmlArrayHandling(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:image" content="http://example.com/rock.jpg">
-<meta property="og:image:width" content="300">
-<meta property="og:image:height" content="300">
-<meta property="og:image" content="http://example.com/rock2.jpg">
-<meta property="og:image" content="http://example.com/rock3.jpg">
-<meta property="og:image:height" content="1000">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:image" content="http://example.com/rock.jpg">
+                    <meta property="og:image:width" content="300">
+                    <meta property="og:image:height" content="300">
+                    <meta property="og:image" content="http://example.com/rock2.jpg">
+                    <meta property="og:image" content="http://example.com/rock3.jpg">
+                    <meta property="og:image:height" content="1000">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
-
-        $this->assertEquals(3, count($res->images));
-        $this->assertEquals("http://example.com/rock.jpg", $res->images[0]->url);
-        $this->assertEquals(300, $res->images[0]->width);
-        $this->assertEquals(300, $res->images[0]->height);
-        $this->assertEquals("http://example.com/rock2.jpg", $res->images[1]->url);
-        $this->assertNull($res->images[1]->width);
-        $this->assertNull($res->images[1]->height);
-        $this->assertEquals("http://example.com/rock3.jpg", $res->images[2]->url);
-        $this->assertNull($res->images[2]->width);
-        $this->assertEquals(1000, $res->images[2]->height);
+        // act
+        $result = $consumer->loadHtml($content);
+
+        // assert
+        self::assertCount(3, $result->images);
+        self::assertSame('http://example.com/rock.jpg', $result->images[0]->url);
+        self::assertSame(300, $result->images[0]->width);
+        self::assertSame(300, $result->images[0]->height);
+        self::assertSame('http://example.com/rock2.jpg', $result->images[1]->url);
+        self::assertNull($result->images[1]->width);
+        self::assertNull($result->images[1]->height);
+        self::assertSame('http://example.com/rock3.jpg', $result->images[2]->url);
+        self::assertNull($result->images[2]->width);
+        self::assertSame(1000, $result->images[2]->height);
     }
 
-    public function testLoadHtmlImages()
+    public function testLoadHtmlImages(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:image" content="http://example.com/rock.jpg">
-<meta property="og:image:secure_url" content="https://example.com/rock.jpg">
-<meta property="og:image:width" content="300">
-<meta property="og:image:height" content="300">
-<meta property="og:image:type" content="image/jpg">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:image" content="http://example.com/rock.jpg">
+                    <meta property="og:image:secure_url" content="https://example.com/rock.jpg">
+                    <meta property="og:image:width" content="300">
+                    <meta property="og:image:height" content="300">
+                    <meta property="og:image:type" content="image/jpg">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals(1, count($res->images));
-        $this->assertEquals("http://example.com/rock.jpg", $res->images[0]->url);
-        $this->assertEquals("https://example.com/rock.jpg", $res->images[0]->secureUrl);
-        $this->assertEquals(300, $res->images[0]->width);
-        $this->assertEquals(300, $res->images[0]->height);
-        $this->assertEquals("image/jpg", $res->images[0]->type);
+        // assert
+        self::assertCount(1, $result->images);
+        self::assertSame('http://example.com/rock.jpg', $result->images[0]->url);
+        self::assertSame('https://example.com/rock.jpg', $result->images[0]->secureUrl);
+        self::assertSame(300, $result->images[0]->width);
+        self::assertSame(300, $result->images[0]->height);
+        self::assertSame('image/jpg', $result->images[0]->type);
     }
 
-    public function testLoadHtmlVideos()
+    public function testLoadHtmlVideos(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:video" content="http://example.com/rock.ogv">
-<meta property="og:video:secure_url" content="https://example.com/rock.ogv">
-<meta property="og:video:width" content="300">
-<meta property="og:video:height" content="300">
-<meta property="og:video:type" content="video/ogv">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:video" content="http://example.com/rock.ogv">
+                    <meta property="og:video:secure_url" content="https://example.com/rock.ogv">
+                    <meta property="og:video:width" content="300">
+                    <meta property="og:video:height" content="300">
+                    <meta property="og:video:type" content="video/ogv">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals(1, count($res->videos));
-        $this->assertEquals("http://example.com/rock.ogv", $res->videos[0]->url);
-        $this->assertEquals("https://example.com/rock.ogv", $res->videos[0]->secureUrl);
-        $this->assertEquals(300, $res->videos[0]->width);
-        $this->assertEquals(300, $res->videos[0]->height);
-        $this->assertEquals("video/ogv", $res->videos[0]->type);
+        // assert
+        self::assertCount(1, $result->videos);
+        self::assertSame('http://example.com/rock.ogv', $result->videos[0]->url);
+        self::assertSame('https://example.com/rock.ogv', $result->videos[0]->secureUrl);
+        self::assertSame(300, $result->videos[0]->width);
+        self::assertSame(300, $result->videos[0]->height);
+        self::assertSame('video/ogv', $result->videos[0]->type);
     }
 
-    public function testLoadHtmlAudios()
+    public function testLoadHtmlAudios(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:audio" content="http://example.com/rock.mp3">
-<meta property="og:audio:secure_url" content="https://example.com/rock.mp3">
-<meta property="og:audio:type" content="audio/mp3">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:audio" content="http://example.com/rock.mp3">
+                    <meta property="og:audio:secure_url" content="https://example.com/rock.mp3">
+                    <meta property="og:audio:type" content="audio/mp3">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals(1, count($res->audios));
-        $this->assertEquals("http://example.com/rock.mp3", $res->audios[0]->url);
-        $this->assertEquals("https://example.com/rock.mp3", $res->audios[0]->secureUrl);
-        $this->assertEquals("audio/mp3", $res->audios[0]->type);
+        // assert
+        self::assertCount(1, $result->audios);
+        self::assertSame('http://example.com/rock.mp3', $result->audios[0]->url);
+        self::assertSame('https://example.com/rock.mp3', $result->audios[0]->secureUrl);
+        self::assertSame('audio/mp3', $result->audios[0]->type);
     }
 
-    public function testCrawlHtmlImageExceptionDebugOff()
+    public function testCrawlHtmlImageExceptionDebugOff(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:image:width" content="300">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:image:width" content="300">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals(0, count($res->images));
+        // assert
+        self::assertCount(0, $result->images);
     }
 
-    public function testCrawlHtmlImageExceptionDebugOn()
+    public function testCrawlHtmlImageExceptionDebugOn(): void
     {
+        // assert
         $this->expectException(\UnexpectedValueException::class);
 
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:image:width" content="300">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:image:width" content="300">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
         $consumer->debug = true;
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $consumer->loadHtml($content);
     }
 
-    public function testCrawlHtmlVideoExceptionDebugOff()
+    public function testCrawlHtmlVideoExceptionDebugOff(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:video:width" content="300">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:video:width" content="300">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals(0, count($res->videos));
+        // assert
+        self::assertCount(0, $result->videos);
     }
 
-    public function testCrawlHtmlVideoExceptionDebugOn()
+    public function testCrawlHtmlVideoExceptionDebugOn(): void
     {
+        // assert
         $this->expectException(\UnexpectedValueException::class);
 
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:video:width" content="300">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:video:width" content="300">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
         $consumer->debug = true;
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $consumer->loadHtml($content);
     }
 
-    public function testCrawlHtmlAudioExceptionDebugOff()
+    public function testCrawlHtmlAudioExceptionDebugOff(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:audio:secure_url" content="300">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:audio:secure_url" content="300">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals(0, count($res->audios));
+        // assert
+        self::assertCount(0, $result->audios);
     }
 
-    public function testCrawlHtmlAudioExceptionDebugOn()
+    public function testCrawlHtmlAudioExceptionDebugOn(): void
     {
+        // assert
         $this->expectException(\UnexpectedValueException::class);
 
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:audio:type" content="audio/mp3">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:audio:type" content="audio/mp3">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
         $consumer->debug = true;
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $consumer->loadHtml($content);
     }
 
-    public function testLoadHtmlSpecialCharacters()
+    public function testLoadHtmlSpecialCharacters(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta property="og:title" content="Apples &amp; Bananas - just &quot;Fruits&quot;">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta property="og:title" content="Apples &amp; Bananas - just &quot;Fruits&quot;">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals("Apples & Bananas - just \"Fruits\"", $res->title);
+        // assert
+        self::assertSame('Apples & Bananas - just "Fruits"', $result->title);
     }
-    
-    public function testReadMetaName()
+
+    public function testReadMetaName(): void
     {
+        // arrange
         $content = <<<LONG
-<html>
-<head>
-<meta name="og:title" content="A 'name' attribute instead of 'property'">
-</head>
-<body></body>
-</html>
-LONG;
+            <html>
+                <head>
+                    <meta name="og:title" content="A 'name' attribute instead of 'property'">
+                </head>
+                <body></body>
+            </html>
+            LONG;
 
         $consumer = new Consumer();
 
-        $res = $consumer->loadHtml($content);
+        // act
+        $result = $consumer->loadHtml($content);
 
-        $this->assertEquals("A 'name' attribute instead of 'property'", $res->title);
+        // assert
+        self::assertSame("A 'name' attribute instead of 'property'", $result->title);
     }
 }
diff --git a/tests/PublisherTest.php b/tests/PublisherTest.php
index 6cb0559..869c4d2 100644
--- a/tests/PublisherTest.php
+++ b/tests/PublisherTest.php
@@ -1,71 +1,80 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Test;
 
-use DateTime;
 use Fusonic\OpenGraph\Publisher;
 use Fusonic\OpenGraph\Test\TestData\TestPublishObject;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
-use stdClass;
-use UnexpectedValueException;
 
-class PublisherTest extends TestCase
+final class PublisherTest extends TestCase
 {
-    /**
-     * @var Publisher
-     */
-    private $publisher;
-
-    protected function setUp(): void
+    public function testGenerateHtmlNull(): void
     {
-        $this->publisher = new Publisher();
+        // arrange
+        $publisher = new Publisher();
 
-        parent::setUp();
-    }
-
-    public function testGenerateHtmlNull()
-    {
         $object = new TestPublishObject(null);
 
-        $result = $this->publisher->generateHtml($object);
+        // act
+        $result = $publisher->generateHtml($object);
 
-        $this->assertEquals("", $result);
+        // assert
+        self::assertSame('', $result);
     }
 
-    public function generateHtmlValuesProvider()
+    #[DataProvider('generateHtmlValuesProvider')]
+    public function testGenerateHtmlValues(int|float|bool|string|\DateTime $value, string $expectedContent): void
     {
-        return [
-            "Boolean true" =>           [ true,                                         "1" ],
-            "Boolean false" =>          [ false,                                        "0" ],
-            "Integer 1" =>              [ 1,                                            "1" ],
-            "Integer -1" =>             [ -1,                                           "-1" ],
-            "Float 1.11111" =>          [ 1.11111,                                      "1.11111" ],
-            "Float -1.11111" =>         [ -1.11111,                                     "-1.11111" ],
-            "DateTime" =>               [ new DateTime("2014-07-21T20:14:00+02:00"),   "2014-07-21T20:14:00+02:00" ],
-            "String" =>                 [ "string",                                     "string" ],
-            "String with quotes" =>     [ "some \" quotes",                             "some &quot; quotes" ],
-            "String with ampersands" => [ "some & ampersand",                           "some &amp; ampersand" ],
-        ];
-    }
+        // arrange
+        $publisher = new Publisher();
 
-    /**
-     * @dataProvider generateHtmlValuesProvider
-     */
-    public function testGenerateHtmlValues($value, $expectedContent)
-    {
         $object = new TestPublishObject($value);
 
-        $result = $this->publisher->generateHtml($object);
+        // act
+        $result = $publisher->generateHtml($object);
 
-        $this->assertEquals('<meta property="' . TestPublishObject::KEY . '" content="' . $expectedContent . '">', $result);
+        // assert
+        self::assertSame(\sprintf('<meta property="%s" content="%s">', TestPublishObject::KEY, $expectedContent), $result);
     }
 
-    public function testGenerateHtmlUnsupportedObject()
+    public function testGenerateHtmlUnsupportedObject(): void
     {
-        $this->expectException(UnexpectedValueException::class);
+        // assert
+        $this->expectException(\UnexpectedValueException::class);
 
-        $object = new TestPublishObject(new stdClass());
+        // arrange
+        $publisher = new Publisher();
+
+        $object = new TestPublishObject(new \stdClass());
+
+        // act
+        $publisher->generateHtml($object);
+    }
 
-        $this->publisher->generateHtml($object);
+    /**
+     * @return array<string, list<int|float|bool|string|\DateTime>>
+     */
+    public static function generateHtmlValuesProvider(): array
+    {
+        return [
+            'Boolean true' => [true, '1'],
+            'Boolean false' => [false, '0'],
+            'Integer 1' => [1, '1'],
+            'Integer -1' => [-1, '-1'],
+            'Float 1.11111' => [1.11111, '1.11111'],
+            'Float -1.11111' => [-1.11111, '-1.11111'],
+            'DateTime' => [new \DateTime('2014-07-21T20:14:00+02:00'), '2014-07-21T20:14:00+02:00'],
+            'String' => ['string', 'string'],
+            'String with quotes' => ['some " quotes', 'some &quot; quotes'],
+            'String with ampersands' => ['some & ampersand', 'some &amp; ampersand'],
+        ];
     }
 }
diff --git a/tests/TestData/TestPublishObject.php b/tests/TestData/TestPublishObject.php
index dd1dcf0..438fbbe 100644
--- a/tests/TestData/TestPublishObject.php
+++ b/tests/TestData/TestPublishObject.php
@@ -1,21 +1,24 @@
 <?php
 
+/*
+ * Copyright (c) Fusonic GmbH. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+
+declare(strict_types=1);
+
 namespace Fusonic\OpenGraph\Test\TestData;
 
 use Fusonic\OpenGraph\Objects\ObjectBase;
 use Fusonic\OpenGraph\Property;
 
-class TestPublishObject extends ObjectBase
+final class TestPublishObject extends ObjectBase
 {
-    const KEY = "og:title";
-
-    private $value;
-
-    public function __construct($value)
-    {
-        parent::__construct();
+    public const KEY = 'og:title';
 
-        $this->value = $value;
+    public function __construct(
+        private readonly mixed $value,
+    ) {
     }
 
     public function getProperties(): array