diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e81e5ba..f58f53f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-versions: ['7.4', '8.0']
+        php-versions: ['8.2', '8.3', '8.4']
     name: PHP ${{ matrix.php-versions }}
     steps:
       - uses: actions/checkout@v2
@@ -22,7 +22,7 @@ jobs:
 
       - name: Cache Composer packages
         id: composer-cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: vendor
           key: composer-${{ hashFiles('**/composer.json') }}
diff --git a/composer.json b/composer.json
index aaa7372..423ece6 100644
--- a/composer.json
+++ b/composer.json
@@ -12,11 +12,11 @@
         }
     },
     "require": {
-        "php": "^7.4|^8.0",
-        "symfony/yaml": "^4.0|^5.0|^6.0|^7.0",
+        "php": "^8.2||^8.3||^8.4",
+        "symfony/yaml": "^7.0",
         "league/commonmark": "^2.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.0"
+        "phpunit/phpunit": "^11.0"
     }
 }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 93a96e8..b9122d8 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -2,15 +2,18 @@
 <!--
     phpunit -c phpunit.xml
 -->
-<phpunit backupGlobals="false"
-         backupStaticAttributes="false"
-         colors="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
-         processIsolation="false"
-         stopOnFailure="false"
-         bootstrap="vendor/autoload.php">
+<phpunit 
+    bootstrap="vendor/autoload.php" 
+    executionOrder="depends,defects" 
+    beStrictAboutOutputDuringTests="true" 
+    failOnDeprecation="true"
+    failOnRisky="true" 
+    failOnWarning="true" 
+    colors="true" 
+    testdox="false"
+    cacheDirectory=".phpunit.cache" 
+    displayDetailsOnTestsThatTriggerDeprecations="true"
+    beStrictAboutCoverageMetadata="true">
 
     <testsuites>
         <testsuite name="Tests">
diff --git a/src/Bridge/CommonMark/CommonMarkParser.php b/src/Bridge/CommonMark/CommonMarkParser.php
index b1fc2c0..dd90e8b 100644
--- a/src/Bridge/CommonMark/CommonMarkParser.php
+++ b/src/Bridge/CommonMark/CommonMarkParser.php
@@ -1,4 +1,6 @@
-<?php declare(strict_types=1);
+<?php
+
+declare(strict_types=1);
 
 namespace Mni\FrontYAML\Bridge\CommonMark;
 
@@ -9,17 +11,17 @@
 /**
  * Bridge to the League CommonMark parser
  */
-class CommonMarkParser implements MarkdownParser
+final class CommonMarkParser implements MarkdownParser
 {
     private MarkdownConverterInterface $parser;
 
-    public function __construct(MarkdownConverterInterface $commonMarkConverter = null)
+    public function __construct(MarkdownConverterInterface|null $commonMarkConverter = null)
     {
-        $this->parser = $commonMarkConverter ?: new CommonMarkConverter;
+        $this->parser = $commonMarkConverter ?: new CommonMarkConverter();
     }
 
     public function parse(string $markdown): string
     {
-        return $this->parser->convertToHtml($markdown)->getContent();
+        return $this->parser?->convertToHtml($markdown)?->getContent() ?? '';
     }
 }
diff --git a/src/Bridge/Symfony/SymfonyYAMLParser.php b/src/Bridge/Symfony/SymfonyYAMLParser.php
index bf22d88..b186ebc 100644
--- a/src/Bridge/Symfony/SymfonyYAMLParser.php
+++ b/src/Bridge/Symfony/SymfonyYAMLParser.php
@@ -8,16 +8,16 @@
 /**
  * Bridge to the Symfony YAML parser
  */
-class SymfonyYAMLParser implements YAMLParser
+final class SymfonyYAMLParser implements YAMLParser
 {
     private Parser $parser;
 
     public function __construct()
     {
-        $this->parser = new Parser;
+        $this->parser = new Parser();
     }
 
-    public function parse(string $yaml)
+    public function parse(string $yaml): mixed
     {
         return $this->parser->parse($yaml);
     }
diff --git a/src/Document.php b/src/Document.php
index 4af4e8d..a80e159 100644
--- a/src/Document.php
+++ b/src/Document.php
@@ -2,10 +2,9 @@
 
 namespace Mni\FrontYAML;
 
-class Document
+final class Document
 {
-    /** @var mixed */
-    private $yaml;
+    private mixed $yaml;
 
     private string $content;
 
@@ -13,7 +12,7 @@ class Document
      * @param mixed $yaml YAML content.
      * @param string $content Content of the document.
      */
-    public function __construct($yaml, string $content)
+    public function __construct(mixed $yaml, string $content)
     {
         $this->yaml = $yaml;
         $this->content = $content;
@@ -22,7 +21,7 @@ public function __construct($yaml, string $content)
     /**
      * @return mixed YAML content.
      */
-    public function getYAML()
+    public function getYAML(): mixed
     {
         return $this->yaml;
     }
diff --git a/src/Parser.php b/src/Parser.php
index 2aa7fd4..8efdfd1 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -7,39 +7,37 @@
 use Mni\FrontYAML\Markdown\MarkdownParser;
 use Mni\FrontYAML\YAML\YAMLParser;
 
+use function array_filter;
+use function array_map;
+use function implode;
+use function ltrim;
+use function preg_match;
+use function preg_quote;
+use function trim;
+
 /**
  * YAML Front matter parser
  */
-class Parser
+final class Parser
 {
-    /**
-     * @var YAMLParser
-     */
-    private $yamlParser;
+    private YAMLParser $yamlParser;
 
-    /**
-     * @var MarkdownParser
-     */
-    private $markdownParser;
+    private MarkdownParser $markdownParser;
 
     private array $startSep;
 
     private array $endSep;
 
-    /**
-     * @param string|string[] $startSep
-     * @param string|string[] $endSep
-     */
     public function __construct(
-        ?YAMLParser $yamlParser = null,
-        ?MarkdownParser $markdownParser = null,
-        $startSep = '---',
-        $endSep = '---'
+        YAMLParser|null $yamlParser = null,
+        MarkdownParser|null $markdownParser = null,
+        string|array $startSep = '---',
+        string|array $endSep = '---'
     ) {
-        $this->yamlParser = $yamlParser ?: new SymfonyYAMLParser;
-        $this->markdownParser = $markdownParser ?: new CommonMarkParser;
-        $this->startSep = array_filter((array) $startSep, 'is_string') ?: ['---'];
-        $this->endSep = array_filter((array) $endSep, 'is_string') ?: ['---'];
+        $this->yamlParser     = $yamlParser ?? new SymfonyYAMLParser();
+        $this->markdownParser = $markdownParser ?? new CommonMarkParser();
+        $this->startSep       = array_filter((array) $startSep, 'is_string') ?: ['---'];
+        $this->endSep         = array_filter((array) $endSep, 'is_string') ?: ['---'];
     }
 
     /**
@@ -51,7 +49,7 @@ public function parse(string $str, bool $parseMarkdown = true): Document
     {
         $yaml = null;
 
-        $quote = static function ($str) {
+        $quote = static function (string $str): string {
             return preg_quote($str, "~");
         };
 
diff --git a/src/YAML/YAMLParser.php b/src/YAML/YAMLParser.php
index 0b4c6c2..4e53efc 100644
--- a/src/YAML/YAMLParser.php
+++ b/src/YAML/YAMLParser.php
@@ -9,8 +9,6 @@ interface YAMLParser
 {
     /**
      * Parses a YAML string.
-     *
-     * @return mixed
      */
-    public function parse(string $yaml);
+    public function parse(string $yaml): mixed;
 }
diff --git a/tests/Bridge/CommonMark/CommonMarkParserTest.php b/tests/Bridge/CommonMark/CommonMarkParserTest.php
index ae2998b..14ab83c 100644
--- a/tests/Bridge/CommonMark/CommonMarkParserTest.php
+++ b/tests/Bridge/CommonMark/CommonMarkParserTest.php
@@ -10,7 +10,7 @@
 
 class CommonMarkParserTest extends TestCase
 {
-    public function testParseWithDefaultParser()
+    public function testParseWithDefaultParser(): void
     {
         $parser = new CommonMarkParser();
 
@@ -19,10 +19,10 @@ public function testParseWithDefaultParser()
         $this->assertSame("<h1>This is a title</h1>\n", $html);
     }
 
-    public function testParseWithCustomParser()
+    public function testParseWithCustomParser(): void
     {
-        $environment = new Environment;
-        $environment->addExtension(new CommonMarkCoreExtension);
+        $environment = new Environment();
+        $environment->addExtension(new CommonMarkCoreExtension());
         $converter = new MarkdownConverter($environment);
 
         $parser = new CommonMarkParser($converter);
diff --git a/tests/FunctionalTest.php b/tests/FunctionalTest.php
index c518cf4..ffb6e48 100644
--- a/tests/FunctionalTest.php
+++ b/tests/FunctionalTest.php
@@ -5,11 +5,13 @@
 use Mni\FrontYAML\Parser;
 use PHPUnit\Framework\TestCase;
 
-class FunctionalTest extends TestCase
+use function str_replace;
+
+final class FunctionalTest extends TestCase
 {
-    public function testSimpleDocument()
+    public function testSimpleDocument(): void
     {
-        $parser = new Parser;
+        $parser = new Parser();
 
         $str = <<<EOF
 ---
@@ -23,9 +25,9 @@ public function testSimpleDocument()
         $this->assertSame("<p>This <strong>strong</strong></p>\n", $document->getContent());
     }
 
-    public function testEscaping()
+    public function testEscaping(): void
     {
-        $parser = new Parser;
+        $parser = new Parser();
 
         $str = <<<EOF
 ---
@@ -52,10 +54,10 @@ public function testEscaping()
         $this->assertSame("<p>Foo</p>\n", $document->getContent());
     }
 
-    public function testMultilineMarkdown()
+    public function testMultilineMarkdown(): void
     {
-        $parser = new Parser;
-        $str = <<<EOF
+        $parser   = new Parser();
+        $str      = <<<EOF
 Foo
 
 Bar
@@ -69,9 +71,9 @@ public function testMultilineMarkdown()
         $this->assertEquals($this->normalizeEOL($expected), $this->normalizeEOL($document->getContent()));
     }
 
-    public function testCrossOsMultiline()
+    public function testCrossOsMultiline(): void
     {
-        $parser = new Parser;
+        $parser  = new Parser();
         $content = <<<EOF
 ---
 lorem: ipsum
@@ -105,10 +107,10 @@ public function testCrossOsMultiline()
         $this->assertSame($this->normalizeEOL($expectedHtml), $this->normalizeEOL($dosYaml['multiline']));
     }
 
-    public function testNonGreedySeparator()
+    public function testNonGreedySeparator(): void
     {
-        $parser = new Parser;
-        $content = <<<EOF
+        $parser   = new Parser();
+        $content  = <<<EOF
 ---
 lorem: ipsum
 ---
@@ -117,10 +119,10 @@ public function testNonGreedySeparator()
 Ipsum
 EOF;
         $document = $parser->parse($content);
-        $this->assertSame(array('lorem' => 'ipsum'), $document->getYAML());
+        $this->assertSame(['lorem' => 'ipsum'], $document->getYAML());
     }
 
-    private function normalizeEOL($str)
+    private function normalizeEOL(string $str): string|array
     {
         return str_replace("\r", '', $str);
     }
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index 056902d..2e54fc2 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -2,14 +2,16 @@
 
 namespace Mni\FrontYAML\Test;
 
+use Mni\FrontYAML\Markdown\MarkdownParser;
 use Mni\FrontYAML\Parser;
-use PHPUnit\Framework\TestCase;
 use Mni\FrontYAML\YAML\YAMLParser;
-use Mni\FrontYAML\Markdown\MarkdownParser;
+use PHPUnit\Framework\TestCase;
+
+use function trim;
 
-class ParserTest extends TestCase
+final class ParserTest extends TestCase
 {
-    public function testParseEmptyString()
+    public function testParseEmptyString(): void
     {
         $parser = new Parser();
         $document = $parser->parse('', false);
@@ -17,7 +19,7 @@ public function testParseEmptyString()
         $this->assertSame('', $document->getContent());
     }
 
-    public function testParseNoYAML()
+    public function testParseNoYAML(): void
     {
         $parser = new Parser();
         $document = $parser->parse('foo', false);
@@ -25,7 +27,7 @@ public function testParseNoYAML()
         $this->assertSame('foo', $document->getContent());
     }
 
-    public function testParseNoYAML2()
+    public function testParseNoYAML2(): void
     {
         $parser = new Parser();
         $str = <<<EOF
@@ -37,7 +39,7 @@ public function testParseNoYAML2()
         $this->assertSame($str, $document->getContent());
     }
 
-    public function testParseFrontYAMLDelimiter()
+    public function testParseFrontYAMLDelimiter(): void
     {
         $parser = new Parser();
         $document = $parser->parse('---', false);
@@ -45,7 +47,7 @@ public function testParseFrontYAMLDelimiter()
         $this->assertSame('---', $document->getContent());
     }
 
-    public function testParseFrontYAMLDelimiters()
+    public function testParseFrontYAMLDelimiters(): void
     {
         $parser = new Parser();
         $str = <<<EOF
@@ -57,7 +59,7 @@ public function testParseFrontYAMLDelimiters()
         $this->assertSame('', $document->getContent());
     }
 
-    public function testParseFrontYAMLPregMatchDelimiter()
+    public function testParseFrontYAMLPregMatchDelimiter(): void
     {
         $parser = new Parser(null, null, '~', '~');
         $str = <<<EOF
@@ -69,15 +71,15 @@ public function testParseFrontYAMLPregMatchDelimiter()
         $this->assertSame('', $document->getContent());
     }
 
-    public function testParseYAML()
+    public function testParseYAML(): void
     {
-        $yamlParser = $this->getMockForAbstractClass(YAMLParser::class);
+        $yamlParser = $this->createMock(YAMLParser::class);
         $yamlParser->expects($this->once())
             ->method('parse')
             ->with('foo')
             ->willReturn('bar');
 
-        $markdownParser = $this->getMockForAbstractClass(MarkdownParser::class);
+        $markdownParser = $this->createMock(MarkdownParser::class);
         $markdownParser->expects($this->never())
             ->method('parse');
 
@@ -95,15 +97,15 @@ public function testParseYAML()
         $this->assertSame('bim', $document->getContent());
     }
 
-    public function testParseYAMLMarkdown()
+    public function testParseYAMLMarkdown(): void
     {
-        $yamlParser = $this->getMockForAbstractClass(YAMLParser::class);
+        $yamlParser = $this->createMock(YAMLParser::class);
         $yamlParser->expects($this->once())
             ->method('parse')
             ->with('foo')
             ->willReturn('bar');
 
-        $markdownParser = $this->getMockForAbstractClass(MarkdownParser::class);
+        $markdownParser = $this->createMock(MarkdownParser::class);
         $markdownParser->expects($this->once())
             ->method('parse')
             ->with('bim')
@@ -123,13 +125,13 @@ public function testParseYAMLMarkdown()
         $this->assertSame('bam', $document->getContent());
     }
 
-    public function testParseMarkdownNoYAML1Line()
+    public function testParseMarkdownNoYAML1Line(): void
     {
-        $yamlParser = $this->getMockForAbstractClass(YAMLParser::class);
+        $yamlParser = $this->createMock(YAMLParser::class);
         $yamlParser->expects($this->never())
             ->method('parse');
 
-        $markdownParser = $this->getMockForAbstractClass(MarkdownParser::class);
+        $markdownParser = $this->createMock(MarkdownParser::class);
         $markdownParser->expects($this->once())
             ->method('parse')
             ->with('bim')
@@ -146,13 +148,13 @@ public function testParseMarkdownNoYAML1Line()
         $this->assertSame('bam', $document->getContent());
     }
 
-    public function testParseMarkdownNoYAML2Lines()
+    public function testParseMarkdownNoYAML2Lines(): void
     {
-        $yamlParser = $this->getMockForAbstractClass(YAMLParser::class);
+        $yamlParser = $this->createMock(YAMLParser::class);
         $yamlParser->expects($this->never())
             ->method('parse');
 
-        $markdownParser = $this->getMockForAbstractClass(MarkdownParser::class);
+        $markdownParser = $this->createMock(MarkdownParser::class);
         $markdownParser->expects($this->once())
             ->method('parse')
             ->willReturn('foo');
@@ -169,11 +171,11 @@ public function testParseMarkdownNoYAML2Lines()
         $this->assertSame('foo', $document->getContent());
     }
 
-    public function testMarkdownParserNotCalled()
+    public function testMarkdownParserNotCalled(): void
     {
-        $yamlParser = $this->getMockForAbstractClass(YAMLParser::class);
+        $yamlParser = $this->createMock(YAMLParser::class);
 
-        $markdownParser = $this->getMockForAbstractClass(MarkdownParser::class);
+        $markdownParser = $this->createMock(MarkdownParser::class);
         $markdownParser->expects($this->never())
             ->method('parse');
 
@@ -181,17 +183,17 @@ public function testMarkdownParserNotCalled()
         $parser->parse('foo', false);
     }
 
-    public function testParseFrontYAMLEdgeCaseDelimiters()
+    public function testParseFrontYAMLEdgeCaseDelimiters(): void
     {
         $start = '*_-\)``.|.``(/-_*';
         $end = '--({@}{._.}{@})--';
-        $yamlParser = $this->getMockForAbstractClass(YAMLParser::class);
+        $yamlParser = $this->createMock(YAMLParser::class);
         $yamlParser->expects($this->once())
             ->method('parse')
             ->with('foo: bar')
             ->willReturn(['foo' => 'bar']);
 
-        $markdownParser = $this->getMockForAbstractClass(MarkdownParser::class);
+        $markdownParser = $this->createMock(MarkdownParser::class);
         $markdownParser->expects($this->never())
             ->method('parse');
 
@@ -203,21 +205,21 @@ public function testParseFrontYAMLEdgeCaseDelimiters()
 bim
 EOF;
         $document = $parser->parse($str, false);
-        $this->assertSame(array('foo' => 'bar'), $document->getYAML());
+        $this->assertSame(['foo' => 'bar'], $document->getYAML());
         $this->assertSame('bim', trim($document->getContent()));
     }
 
-    public function testParseFrontYAMLArrayDelimiters()
+    public function testParseFrontYAMLArrayDelimiters(): void
     {
         $start = ['---','<!--'];
         $end = ['---','-->'];
-        $yamlParser = $this->getMockForAbstractClass(YAMLParser::class);
+        $yamlParser = $this->createMock(YAMLParser::class);
         $yamlParser->expects($this->exactly(2))
             ->method('parse')
             ->with('foo: bar')
             ->willReturn(['foo' => 'bar']);
 
-        $markdownParser = $this->getMockForAbstractClass(MarkdownParser::class);
+        $markdownParser = $this->createMock(MarkdownParser::class);
         $markdownParser->expects($this->never())
             ->method('parse');
 
@@ -236,7 +238,7 @@ public function testParseFrontYAMLArrayDelimiters()
 EOF;
         $document1 = $parser->parse($str1, false);
         $document2 = $parser->parse($str2, false);
-        $this->assertSame(array('foo' => 'bar'), $document1->getYAML());
+        $this->assertSame(['foo' => 'bar'], $document1->getYAML());
         $this->assertSame('bim', trim($document1->getContent()));
         $this->assertSame($document1->getYAML(), $document2->getYAML());
         $this->assertSame($document1->getContent(), $document2->getContent());