diff --git a/.github/workflows/phpunit.yml b/.github/workflows/phpunit.yml
new file mode 100644
index 0000000..fe1ae53
--- /dev/null
+++ b/.github/workflows/phpunit.yml
@@ -0,0 +1,38 @@
+name: PHPUnit Tests
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Validate composer.json and composer.lock
+      run: composer validate --strict
+
+    - name: Cache Composer packages
+      id: composer-cache
+      uses: actions/cache@v3
+      with:
+        path: vendor
+        key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-php-
+
+    - name: Build the Docker image
+      run: make build
+
+    - name: Install dependencies
+      run: make install
+
+    - name: Run test suite
+      run: make test
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index c76a9ff..3f58acd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
-.php_cs.cache
+.*.cache
 /.idea/
 /vendor/
 composer.lock
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
new file mode 100644
index 0000000..b33e48c
--- /dev/null
+++ b/.php-cs-fixer.dist.php
@@ -0,0 +1,25 @@
+<?php
+
+return new PhpCsFixer\Config()
+    ->setRiskyAllowed(true)
+    ->setRules([
+        '@PSR12' => true,
+        '@Symfony' => true,
+        'array_indentation' => true,
+        'array_syntax' => ['syntax' => 'short'],
+        'concat_space' => ['spacing' => 'one'],
+        'declare_strict_types' => true,
+        'string_implicit_backslashes' => true,
+        'list_syntax' => ['syntax' => 'short'],
+        'multiline_whitespace_before_semicolons' => ['strategy' => 'new_line_for_chained_calls'],
+        'ordered_imports' => true,
+        'phpdoc_to_comment' => false,
+        'trailing_comma_in_multiline' => ['elements' => ['arrays', 'arguments', 'parameters']],
+        'visibility_required' => ['elements' => ['property', 'method', 'const']],
+    ])
+    ->setFinder(
+        PhpCsFixer\Finder::create()
+            ->in(__DIR__ . '/src')
+            ->in(__DIR__ . '/tests')
+    )
+;
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..40d0ebe
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,36 @@
+FROM php:8.4-cli
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y \
+    git \
+    unzip \
+    libssl-dev \
+    libcurl4-openssl-dev \
+    pkg-config \
+    openjdk-17-jre-headless \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install MongoDB extension
+RUN pecl install mongodb \
+    && docker-php-ext-enable mongodb \
+    && docker-php-ext-install pcntl
+
+# Copy Composer from official image
+COPY --from=composer:latest /usr/bin/composer /usr/bin/composer
+
+# Set working directory
+WORKDIR /app
+
+# Copy composer files
+COPY composer.json composer.lock* ./
+
+# Install dependencies including dev dependencies for testing
+RUN composer install --optimize-autoloader
+
+# Copy application code
+COPY . .
+
+# Set environment variable for Composer
+ENV COMPOSER_ALLOW_SUPERUSER=1
+
+CMD ["tail", "-f", "/dev/null"]
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..30a5db2
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,44 @@
+.PHONY: build up down test phpstan fix-cs install update shell logs clean
+
+# Build the Docker image
+build:
+	docker compose build
+
+# Start the services
+up:
+	docker compose up -d
+
+# Stop the services
+down:
+	docker compose down
+
+# Install dependencies
+install:
+	docker compose run --rm php composer install
+
+# Update dependencies
+update:
+	docker compose run --rm php composer update
+
+# Run all tests
+test: up
+	docker compose exec php vendor/bin/phpunit
+
+phpstan: up
+	docker compose exec php vendor/bin/phpstan
+
+fix-cs: up
+	docker compose exec php vendor/bin/php-cs-fixer fix -v
+
+# Open a shell in the PHP container
+shell:
+	docker compose exec php bash
+
+# View logs
+logs:
+	docker compose logs -f php
+
+# Clean up containers and volumes
+clean:
+	docker compose down -v
+	docker compose rm -f
diff --git a/compose.yaml b/compose.yaml
new file mode 100644
index 0000000..5509e13
--- /dev/null
+++ b/compose.yaml
@@ -0,0 +1,8 @@
+services:
+  php:
+    build: .
+    working_dir: /app
+    volumes:
+      - .:/app
+    environment:
+      - COMPOSER_ALLOW_SUPERUSER=1
diff --git a/composer.json b/composer.json
index bf99c35..556a02a 100644
--- a/composer.json
+++ b/composer.json
@@ -1,31 +1,35 @@
 {
   "name": "recruiterphp/geezer",
   "description": "PHP tools to build robust long-running processes",
+  "license": "MIT",
   "type": "library",
-  "license": "proprietary",
   "authors": [
     {
       "name": "Easy Welfare Development Team",
       "email": "dev@easywelfare.com"
+    },
+    {
+      "name": "Contributors",
+      "homepage": "https://github.com/recruiterphp/geezer/graphs/contributors"
     }
   ],
   "require": {
-    "php": "^7.2",
+    "php": "^8.4",
     "ext-pcntl": "*",
-    "symfony/console": "~4.0",
-    "recruiterphp/concurrency": "^3.0.0"
+    "recruiterphp/concurrency": "^4.0",
+    "symfony/console": "^7.3"
   },
   "require-dev": {
-    "phpunit/phpunit": "^7",
-    "friendsofphp/php-cs-fixer": "^2.13",
-    "phpstan/phpstan": "^0.10.5",
-    "phpstan/phpstan-phpunit": "^0.10.0"
+    "ergebnis/composer-normalize": "^2.47",
+    "friendsofphp/php-cs-fixer": "^3.85",
+    "phpstan/phpstan": "^2.1",
+    "phpunit/phpunit": "^12.3",
+    "rector/rector": "^2.1"
   },
   "provide": {
-    "easywelfare/geezer-implementation": "2.0.0"
+    "easywelfare/geezer-implementation": "self.version"
   },
-  "minimum-stability": "dev",
-  "prefer-stable": true,
+  "minimum-stability": "stable",
   "autoload": {
     "psr-4": {
       "Recruiter\\Geezer\\": "src",
@@ -36,5 +40,11 @@
     "psr-4": {
       "Recruiter\\Geezer\\": "tests"
     }
+  },
+  "config": {
+    "allow-plugins": {
+      "ergebnis/composer-normalize": true,
+      "sort-packages": true
+    }
   }
 }
diff --git a/phpstan.neon b/phpstan.neon
index cc85d47..130e9ca 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,8 +1,5 @@
-includes:
-  - ./vendor/phpstan/phpstan-phpunit/extension.neon
-  - ./vendor/phpstan/phpstan-phpunit/rules.neon
-
 parameters:
-  level: 7
-  excludes_analyse:
-    - %currentWorkingDirectory%/vendor/
+  level: 10
+  paths:
+    - src
+    - tests
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..296ff04
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/12.3/phpunit.xsd"
+         backupGlobals="false"
+         colors="true"
+         displayDetailsOnTestsThatTriggerDeprecations="true"
+         displayDetailsOnPhpunitDeprecations="true"
+         bootstrap="vendor/autoload.php" cacheDirectory=".phpunit.cache">
+    <testsuites>
+        <testsuite name="Test Suite">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory>src</directory>
+        </include>
+    </source>
+</phpunit>
diff --git a/rector.php b/rector.php
new file mode 100644
index 0000000..9400286
--- /dev/null
+++ b/rector.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+
+return RectorConfig::configure()
+    ->withPaths([
+        __DIR__ . '/src',
+        __DIR__ . '/tests',
+    ])
+    // uncomment to reach your current PHP version
+    // ->withPhpSets()
+    ->withTypeCoverageLevel(0)
+    ->withDeadCodeLevel(0)
+    ->withCodeQualityLevel(0);
diff --git a/src/Command/LeadershipEventsHandler.php b/src/Command/LeadershipEventsHandler.php
index fbcb4b9..8b65124 100644
--- a/src/Command/LeadershipEventsHandler.php
+++ b/src/Command/LeadershipEventsHandler.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Command;
 
 interface LeadershipEventsHandler
diff --git a/src/Command/RobustCommand.php b/src/Command/RobustCommand.php
index 4245568..6223042 100644
--- a/src/Command/RobustCommand.php
+++ b/src/Command/RobustCommand.php
@@ -1,12 +1,13 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Command;
 
 use Recruiter\Geezer\Leadership\LeadershipStrategy;
 use Recruiter\Geezer\Timing\WaitStrategy;
 use Symfony\Component\Console\Input\InputDefinition;
 use Symfony\Component\Console\Input\InputInterface;
-use Throwable;
 
 interface RobustCommand
 {
@@ -35,5 +36,5 @@ public function execute(): bool;
     /**
      * @return bool true on successful shutdown, false otherwhise
      */
-    public function shutdown(?Throwable $e = null): bool;
+    public function shutdown(?\Throwable $e = null): bool;
 }
diff --git a/src/Command/RobustCommandRunner.php b/src/Command/RobustCommandRunner.php
index f5f7376..f817252 100644
--- a/src/Command/RobustCommandRunner.php
+++ b/src/Command/RobustCommandRunner.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Command;
 
 use Psr\Log\LoggerInterface;
@@ -8,53 +10,37 @@
 use Symfony\Component\Console\Command\Command;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
-use Throwable;
 
 class RobustCommandRunner extends Command
 {
-    private const CYCLES_BEFORE_GC = 100;
+    private const int CYCLES_BEFORE_GC = 100;
 
-    private const LEADERSHIP_STATUS_ACQUIRED = 'acquired';
-    private const LEADERSHIP_STATUS_LOST = 'lost';
+    private const string LEADERSHIP_STATUS_ACQUIRED = 'acquired';
+    private const string LEADERSHIP_STATUS_LOST = 'lost';
 
-    private const STOP_SIGNALS = [
+    private const array STOP_SIGNALS = [
         SIGINT,
         SIGQUIT,
         SIGTERM,
         SIGHUP,
     ];
 
-    /**
-     * @var RobustCommand
-     */
-    private $wrapped;
+    private bool $askedToStop = false;
 
-    /**
-     * @var LoggerInterface
-     */
-    private $logger;
+    private int $garbageCollectorCounter = 0;
 
-    /**
-     * @var bool
-     */
-    private $askedToStop = false;
+    private ?string $leadershipStatus;
 
-    private $garbageCollectorCounter = 0;
-
-    private $leadershipStatus = null;
-
-    public function __construct(RobustCommand $wrapped, LoggerInterface $logger)
+    public function __construct(private readonly RobustCommand $wrapped, private readonly LoggerInterface $logger)
     {
         parent::__construct($wrapped->name());
 
-        $this->wrapped = $wrapped;
-        $this->logger = $logger;
         $this->setDescription($wrapped->description());
         $this->setDefinition($wrapped->definition());
         $this->leadershipStatus = null;
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $this->wrapped->init($input);
         $this->registerSignalHandlers();
@@ -77,7 +63,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
 
             try {
                 $success = $this->wrapped->execute();
-            } catch (Throwable $e) {
+            } catch (\Throwable $e) {
                 $this->log('Thrown an Exception: ' . get_class($e), ['exception' => $e], LogLevel::ERROR);
                 $occuredException = $e;
 
@@ -102,21 +88,23 @@ protected function execute(InputInterface $input, OutputInterface $output)
         $leadershipStrategy->release();
 
         if ($occuredException) {
-            exit(2);
+            return self::FAILURE;
         }
+
+        return self::SUCCESS;
     }
 
-    private function leadershipWasAcquired()
+    private function leadershipWasAcquired(): void
     {
         $this->leadershipStatusChanged(self::LEADERSHIP_STATUS_ACQUIRED, 'leadershipAcquired');
     }
 
-    private function leadershipWasLost()
+    private function leadershipWasLost(): void
     {
         $this->leadershipStatusChanged(self::LEADERSHIP_STATUS_LOST, 'leadershipLost');
     }
 
-    private function leadershipStatusChanged($newLeadershipStatus, string $hook)
+    private function leadershipStatusChanged(?string $newLeadershipStatus, string $hook): void
     {
         if ($this->leadershipStatus === $newLeadershipStatus) {
             return;
@@ -134,13 +122,13 @@ private function leadershipStatusChanged($newLeadershipStatus, string $hook)
     private function registerSignalHandlers(): void
     {
         foreach (self::STOP_SIGNALS as $signal) {
-            pcntl_signal($signal, function () {
+            pcntl_signal($signal, function (): void {
                 $this->askedToStop = true;
             });
         }
     }
 
-    private function askedToStop()
+    private function askedToStop(): bool
     {
         if (!$this->askedToStop) {
             pcntl_signal_dispatch();
@@ -152,7 +140,7 @@ private function askedToStop()
     private function sleepIfNotAskedToStop(int $milliSeconds): bool
     {
         $microSeconds = $milliSeconds * 1000;
-        for ($i = 0; $i < $microSeconds && !$this->askedToStop(); $i = $i + 50000) {
+        for ($i = 0; $i < $microSeconds && !$this->askedToStop(); $i += 50000) {
             usleep(50000);
         }
 
@@ -165,15 +153,16 @@ private function sleepAccordingTo(WaitStrategy $waitStrategy): void
         $waitStrategy->next();
     }
 
-    private function possiblyCollectGarbage(): int
+    private function possiblyCollectGarbage(): void
     {
         if (0 === (++$this->garbageCollectorCounter % self::CYCLES_BEFORE_GC)) {
-            return gc_collect_cycles();
+            gc_collect_cycles();
         }
-
-        return 0;
     }
 
+    /**
+     * @param array<mixed> $extra
+     */
     private function log(string $message, array $extra = [], string $level = LogLevel::DEBUG): void
     {
         $this->logger->log($level, "[{hostname}:{pid}] $message", array_merge([
diff --git a/src/Leadership/Anarchy.php b/src/Leadership/Anarchy.php
index aa5b5cc..b794cf5 100644
--- a/src/Leadership/Anarchy.php
+++ b/src/Leadership/Anarchy.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Leadership;
 
 class Anarchy implements LeadershipStrategy
diff --git a/src/Leadership/Dictatorship.php b/src/Leadership/Dictatorship.php
index 6f1e35b..4123219 100644
--- a/src/Leadership/Dictatorship.php
+++ b/src/Leadership/Dictatorship.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Leadership;
 
 use Recruiter\Concurrency\Lock;
@@ -19,9 +21,6 @@ class Dictatorship implements LeadershipStrategy
 
     /**
      * Dictatorship constructor.
-     *
-     * @param Lock $lock
-     * @param int  $termOfOffice
      */
     public function __construct(Lock $lock, int $termOfOffice)
     {
diff --git a/src/Leadership/LeadershipStrategy.php b/src/Leadership/LeadershipStrategy.php
index 6b0e9d7..2b04328 100644
--- a/src/Leadership/LeadershipStrategy.php
+++ b/src/Leadership/LeadershipStrategy.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Leadership;
 
 interface LeadershipStrategy
diff --git a/src/Timing/ConstantPause.php b/src/Timing/ConstantPause.php
index 8f47203..ee88c19 100644
--- a/src/Timing/ConstantPause.php
+++ b/src/Timing/ConstantPause.php
@@ -1,18 +1,14 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Timing;
 
 class ConstantPause implements WaitStrategy
 {
-    /**
-     * @var int
-     */
-    private $attempt = 0;
+    private int $attempt = 0;
 
-    /**
-     * @var int
-     */
-    private $pause;
+    private int $pause;
 
     /**
      * ConstantPause constructor.
@@ -26,8 +22,6 @@ public function __construct(int $pause)
 
     /**
      * Number of milliseconds to wait.
-     *
-     * @return int
      */
     public function current(): int
     {
@@ -42,9 +36,6 @@ public function current(): int
      * Return the key of the current element.
      *
      * @see https://php.net/manual/en/iterator.key.php
-     *
-     * @return int
-     *
      * @since 5.0.0
      */
     public function key(): int
@@ -84,7 +75,7 @@ public function rewind(): void
      * @see https://php.net/manual/en/iterator.next.php
      * @since 5.0.0
      */
-    public function next()
+    public function next(): void
     {
         ++$this->attempt;
     }
diff --git a/src/Timing/ExponentialBackoffStrategy.php b/src/Timing/ExponentialBackoffStrategy.php
index 1e3f2c5..4f4c54e 100644
--- a/src/Timing/ExponentialBackoffStrategy.php
+++ b/src/Timing/ExponentialBackoffStrategy.php
@@ -1,23 +1,12 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Recruiter\Geezer\Timing;
 
 class ExponentialBackoffStrategy implements WaitStrategy
 {
-    /**
-     * @var int
-     */
-    private $attempt = 0;
-
-    /**
-     * @var int
-     */
-    private $from;
-
-    /**
-     * @var int
-     */
-    private $to;
+    private int $attempt = 0;
 
     /**
      * ExponentialBackoffStrategy constructor.
@@ -25,16 +14,12 @@ class ExponentialBackoffStrategy implements WaitStrategy
      * @param int $from minimum milliseconds to wait (on second attempt)
      * @param int $to   maximum milliseconds to wait
      */
-    public function __construct(int $from, int $to)
+    public function __construct(private readonly int $from, private readonly int $to)
     {
-        $this->from = $from;
-        $this->to = $to;
     }
 
     /**
      * Number of milliseconds to wait.
-     *
-     * @return int
      */
     public function current(): int
     {
@@ -44,7 +29,7 @@ public function current(): int
 
         return intval(min(
             2 ** ($this->attempt - 1) * $this->from,
-            $this->to
+            $this->to,
         ));
     }
 
@@ -52,9 +37,6 @@ public function current(): int
      * Return the key of the current element.
      *
      * @see https://php.net/manual/en/iterator.key.php
-     *
-     * @return int
-     *
      * @since 5.0.0
      */
     public function key(): int
@@ -94,7 +76,7 @@ public function rewind(): void
      * @see https://php.net/manual/en/iterator.next.php
      * @since 5.0.0
      */
-    public function next()
+    public function next(): void
     {
         ++$this->attempt;
     }
diff --git a/src/Timing/WaitStrategy.php b/src/Timing/WaitStrategy.php
index 252669e..92bfd44 100644
--- a/src/Timing/WaitStrategy.php
+++ b/src/Timing/WaitStrategy.php
@@ -1,15 +1,16 @@
 <?php
 
-namespace Recruiter\Geezer\Timing;
+declare(strict_types=1);
 
-use Iterator;
+namespace Recruiter\Geezer\Timing;
 
-interface WaitStrategy extends Iterator
+/**
+ * @extends \Iterator<int, int>
+ */
+interface WaitStrategy extends \Iterator
 {
     /**
      * Number of milliseconds to wait.
-     *
-     * @return int
      */
     public function current(): int;
 }
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 7a9986c..e2741fe 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 $autoloadFile = __DIR__ . '/../vendor/autoload.php';
 if (!is_readable($autoloadFile)) {
     throw new RuntimeException('Autoloader not found, did you run composer install?');
diff --git a/tests/unit/Timing/ExponentialBackoffStrategyTest.php b/tests/unit/Timing/ExponentialBackoffStrategyTest.php
index 864aeb7..5173975 100644
--- a/tests/unit/Timing/ExponentialBackoffStrategyTest.php
+++ b/tests/unit/Timing/ExponentialBackoffStrategyTest.php
@@ -1,13 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Test\Geezer\Timing;
 
-use Recruiter\Geezer\Timing\ExponentialBackoffStrategy;
 use PHPUnit\Framework\TestCase;
+use Recruiter\Geezer\Timing\ExponentialBackoffStrategy;
 
 class ExponentialBackoffStrategyTest extends TestCase
 {
-    public function testNextWorksCorrectly()
+    public function testNextWorksCorrectly(): void
     {
         $strategy = new ExponentialBackoffStrategy(100, 1000);
         $this->assertEquals(0, $strategy->current());