diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 671a5a8..c58fede 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -7,32 +7,57 @@ on:
   pull_request:
     branches: [ master ]
 
+permissions:
+  contents: read
+
 jobs:
   run:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       #for each of the following versions of PHP, with and without --prefer-lowest
       matrix:
-        php-versions: ['5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4']
-
+        php-versions: ['7.2.5', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
+        composer-options: ['', '--prefer-lowest']
     #set the name for each job
-    name: PHP ${{ matrix.php-versions }}
+    name: PHP ${{ matrix.php-versions }} ${{ matrix.composer-options }}
+    #set up environment variables used by unit tests
+    env:
+      AWS_ACCESS_KEY_ID: foo
+      AWS_SECRET_ACCESS_KEY: bar
+      AWS_CSM_ENABLED: false
+      AWS_SUPPRESS_PHP_DEPRECATION_WARNING: true
     steps:
       #sets up the correct version of PHP with necessary config options
-      - name: Setup PHP
+      - name: Setup PHP with Xdebug
         uses: shivammathur/setup-php@v2
         with:
+          coverage: xdebug
           php-version: ${{ matrix.php-versions }}
-          ini-values: memory_limit=4G, phar.readonly=false
+          ini-values: xdebug.overload_var_dump=0, memory_limit=4G, phar.readonly=false
 
       #checkout the codebase from github
       - name: Checkout codebase
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
+
+      #validate composer files
+      - name: Validate composer.json and composer.lock
+        run: composer validate
 
-      #run composer
-      - name: Composer install
-        run: composer install
+      #get dependencies
+      - name: Install dependencies
+        run: composer update ${{ matrix.composer-options }} --no-interaction --prefer-source
+
+      #php 8.x requirements
+      - if: ${{ matrix.php-versions >= '8.0' && matrix.composer-options != '' }}
+        name: PHP 8.x
+        run: composer require --dev phpunit/phpunit "^9.5" --no-interaction --prefer-source --with-all-dependencies
+
+      #php 8.1+ requirements
+      - if: ${{ matrix.php-versions >= '8.1' && matrix.composer-options != '' }}
+        name: PHP 8.1+
+        run: composer require --dev guzzlehttp/guzzle "^7.4.5" --no-interaction --prefer-source --with-all-dependencies
 
       #run tests
       - name: Run test suite
-        run: vendor/bin/phpunit
\ No newline at end of file
+        run: make test
+
diff --git a/composer.json b/composer.json
index 9f9240d..2c37c14 100644
--- a/composer.json
+++ b/composer.json
@@ -12,16 +12,16 @@
         }
     ],
     "require": {
-        "php": ">=5.5",
-        "aws/aws-sdk-php": "^3.2.6",
-        "symfony/config": "~2.3|~3.0|~4.0|~5.0|~6.0",
-        "symfony/dependency-injection": "~2.3|~3.0|~4.0|~5.0|~6.0",
-        "symfony/http-kernel": "~2.3|~3.0|~4.0|~5.0|~6.0"
+        "php": ">=7.2.5",
+        "aws/aws-sdk-php": "^3.279.0",
+        "symfony/config": "~5.0|~6.0|~7.0",
+        "symfony/dependency-injection": "~5.0|~6.0|~7.0",
+        "symfony/http-kernel": "~5.0|~6.0|~7.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35|^5.6.3|^6.0.0",
-        "symfony/framework-bundle": "~2.3|~3.0|~4.0|~5.0|~6.0",
-        "symfony/yaml": "~2.3|~3.0|~4.0|~5.0|~6.0"
+        "phpunit/phpunit": "^8.5|^9.5",
+        "symfony/framework-bundle": "~5.0|~6.0|~7.0",
+        "symfony/yaml": "~5.0|~6.0|~7.0"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/DependencyInjection/AwsExtension.php b/src/DependencyInjection/AwsExtension.php
index c51ac76..b496eb5 100644
--- a/src/DependencyInjection/AwsExtension.php
+++ b/src/DependencyInjection/AwsExtension.php
@@ -15,7 +15,10 @@
 
 class AwsExtension extends Extension
 {
-    public function load(array $configs, ContainerBuilder $container)
+    /**
+     * @throws \Exception
+     */
+    public function load(array $configs, ContainerBuilder $container): void
     {
         $loader = new YamlFileLoader(
             $container,
@@ -44,7 +47,7 @@ public function load(array $configs, ContainerBuilder $container)
     }
 
 
-    private function createServiceDefinition($name)
+    private function createServiceDefinition($name): Definition
     {
         $clientClass = "Aws\\{$name}\\{$name}Client";
         $serviceDefinition = new Definition(
@@ -53,21 +56,13 @@ class_exists($clientClass) ? $clientClass : AwsClient::class
 
         $serviceDefinition->setLazy(true);
 
-        // Handle Symfony >= 2.6
-        if (method_exists($serviceDefinition, 'setFactory')) {
-            return $serviceDefinition->setFactory([
-                new Reference('aws_sdk'),
-                'createClient',
-            ])->setArguments([$name]);
-        }
-
-        return $serviceDefinition
-                ->setFactoryService('aws_sdk')
-                ->setFactoryMethod('createClient')
-                ->setArguments([$name]);
+        return $serviceDefinition->setFactory([
+            new Reference('aws_sdk'),
+            'createClient',
+        ])->setArguments([$name]);
     }
 
-    private function inflateServicesInConfig(array &$config)
+    private function inflateServicesInConfig(array &$config): void
     {
         array_walk($config, function (&$value) {
             if (is_array($value)) {
diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
index 6dc866f..2a13fbe 100644
--- a/src/DependencyInjection/Configuration.php
+++ b/src/DependencyInjection/Configuration.php
@@ -8,7 +8,7 @@
 
 class Configuration implements ConfigurationInterface
 {
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         // Maintain backwars compatibility, only merge when AWS_MERGE_CONFIG is set
         $mergeConfig = $this->shouldMergeConfig();
@@ -70,8 +70,7 @@ public function getConfigTreeBuilder()
                 ->variableNode('ua_append')->end()
                 ->variableNode('validate')->end()
                 ->scalarNode('version')->end()
-            ->end()
-        ;
+            ->end();
 
         //Setup config trees for each of the services
         foreach (array_column(Aws\manifest(), 'namespace') as $awsService) {
@@ -111,14 +110,13 @@ public function getConfigTreeBuilder()
                             ->scalarNode('version')->end()
                         ->end()
                     ->end()
-                ->end()
-            ;
+                ->end();
         }
 
         return $treeBuilder;
     }
 
-    protected function shouldMergeConfig()
+    protected function shouldMergeConfig(): ?string
     {
         # works with symfony/dotenv
         if (isset($_ENV['AWS_MERGE_CONFIG'])) {
diff --git a/tests/DependencyInjection/AwsExtensionTest.php b/tests/DependencyInjection/AwsExtensionTest.php
index 6c9fd1b..7db8c61 100644
--- a/tests/DependencyInjection/AwsExtensionTest.php
+++ b/tests/DependencyInjection/AwsExtensionTest.php
@@ -10,6 +10,7 @@
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\DependencyInjection\Definition;
 use Symfony\Component\DependencyInjection\Reference;
 
 class AwsExtensionTest extends TestCase
@@ -24,7 +25,7 @@ class AwsExtensionTest extends TestCase
      */
     protected $container;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->kernel = new AppKernel('test', true);
         $this->kernel->boot();
@@ -38,9 +39,9 @@ public function setUp()
     public function sdk_config_should_be_passed_directly_to_the_constructor_and_resolved_by_the_sdk()
     {
         $config           = $this->kernel->getTestConfig()['aws'];
-        $s3Region         = isset($config['S3']['region']) ? $config['S3']['region'] : $config['region'];
-        $lambdaRegion     = isset($config['Lambda']['region']) ? $config['Lambda']['region'] : $config['region'];
-        $codeDeployRegion = isset($config['CodeDeploy']['region']) ? $config['CodeDeploy']['region'] : $config['region'];
+        $s3Region         = $config['S3']['region'] ?? $config['region'];
+        $lambdaRegion     = $config['Lambda']['region'] ?? $config['region'];
+        $codeDeployRegion = $config['CodeDeploy']['region'] ?? $config['region'];
 
         $testService = $this->container->get('test_service');
 
@@ -76,13 +77,16 @@ public function extension_should_escape_strings_that_begin_with_at_sign()
             'secret' => '@@secret'
         ]];
         $container = $this->getMockBuilder(ContainerBuilder::class)
-            ->setMethods(['getDefinition', 'replaceArgument'])
+            ->onlyMethods(['getDefinition'])
+            ->getMock();
+        $definition = $this->getMockBuilder(Definition::class)
+            ->onlyMethods(['replaceArgument'])
             ->getMock();
         $container->expects($this->once())
             ->method('getDefinition')
             ->with('aws_sdk')
-            ->willReturnSelf();
-        $container->expects($this->once())
+            ->willReturn($definition);
+        $definition->expects($this->once())
             ->method('replaceArgument')
             ->with(0, $this->callback(function ($arg) {
                 return is_array($arg)
@@ -104,13 +108,16 @@ public function extension_should_expand_service_references()
         $extension = new AwsExtension;
         $config = ['credentials' => '@aws_sdk'];
         $container = $this->getMockBuilder(ContainerBuilder::class)
-            ->setMethods(['getDefinition', 'replaceArgument'])
+            ->onlyMethods(['getDefinition'])
+            ->getMock();
+        $definition = $this->getMockBuilder(Definition::class)
+            ->onlyMethods(['replaceArgument'])
             ->getMock();
         $container->expects($this->once())
             ->method('getDefinition')
             ->with('aws_sdk')
-            ->willReturnSelf();
-        $container->expects($this->once())
+            ->willReturn($definition);
+        $definition->expects($this->once())
             ->method('replaceArgument')
             ->with(0, $this->callback(function ($arg) {
                 return is_array($arg)
@@ -137,7 +144,6 @@ public function extension_should_validate_and_merge_configs()
             'stats' => [
                 'http' => true
             ],
-            'retries' => 5,
             'endpoint' => 'http://localhost:8000',
             'endpoint_discovery' => [
                 'enabled' => true,
@@ -181,13 +187,16 @@ public function extension_should_validate_and_merge_configs()
             'validate' => true,
         ];
         $container = $this->getMockBuilder(ContainerBuilder::class)
-            ->setMethods(['getDefinition', 'replaceArgument'])
+            ->onlyMethods(['getDefinition'])
+            ->getMock();
+        $definition = $this->getMockBuilder(Definition::class)
+            ->onlyMethods(['replaceArgument'])
             ->getMock();
         $container->expects($this->once())
             ->method('getDefinition')
             ->with('aws_sdk')
-            ->willReturnSelf();
-        $container->expects($this->once())
+            ->willReturn($definition);
+        $definition->expects($this->once())
             ->method('replaceArgument')
             ->with(0, $this->callback(function ($arg) {
                 return is_array($arg)
@@ -230,9 +239,8 @@ public function extension_should_error_merging_unknown_config_options()
             'foo' => 'baz'
         ];
         $container = $this->getMockBuilder(ContainerBuilder::class)
-            ->setMethods(['getDefinition', 'replaceArgument'])
+            ->onlyMethods(['getDefinition'])
             ->getMock();
-
         try {
             $extension->load([$config, $configDev], $container);
             $this->fail('Should have thrown an Error or RuntimeException');
diff --git a/tests/DependencyInjection/ConfigurationTest.php b/tests/DependencyInjection/ConfigurationTest.php
index 49e2454..ef66fdc 100644
--- a/tests/DependencyInjection/ConfigurationTest.php
+++ b/tests/DependencyInjection/ConfigurationTest.php
@@ -10,7 +10,7 @@
 
 class ConfigurationTest extends TestCase
 {
-    public function setUp()
+    public function setUp(): void
     {
         (new Filesystem)
             ->remove(implode(DIRECTORY_SEPARATOR, [
@@ -39,7 +39,7 @@ public function container_should_compile_and_load($format)
         $this->assertNotInstanceOf(DynamoDbClient::class, $testService->getCodeDeployClient());
     }
 
-    public function formatProvider()
+    public function formatProvider(): array
     {
         return [
             ['yml'],
diff --git a/tests/fixtures/AppKernel.php b/tests/fixtures/AppKernel.php
index 733d86d..b3f79f6 100644
--- a/tests/fixtures/AppKernel.php
+++ b/tests/fixtures/AppKernel.php
@@ -16,7 +16,7 @@ public function __construct($env, $debug, $extension = 'yml')
         parent::__construct($env, $debug);
     }
 
-    public function registerBundles()
+    public function registerBundles(): iterable
     {
         return [
             new FrameworkBundle(),
@@ -24,7 +24,7 @@ public function registerBundles()
         ];
     }
 
-    public function registerContainerConfiguration(LoaderInterface $loader)
+    public function registerContainerConfiguration(LoaderInterface $loader): void
     {
         $loader->load($this->getTestConfigFile($this->extension));
     }
@@ -35,7 +35,7 @@ public function getTestConfig()
     }
 
 
-    private function getTestConfigFile($extension)
+    private function getTestConfigFile($extension): string
     {
         return __DIR__ . '/config.' . $extension;
     }
diff --git a/tests/fixtures/TestService.php b/tests/fixtures/TestService.php
index 8f48792..2a7868b 100644
--- a/tests/fixtures/TestService.php
+++ b/tests/fixtures/TestService.php
@@ -35,7 +35,7 @@ public function __construct(
     /**
      * @return S3Client
      */
-    public function getS3Client()
+    public function getS3Client(): S3Client
     {
         return $this->s3Client;
     }
@@ -43,7 +43,7 @@ public function getS3Client()
     /**
      * @return LambdaClient
      */
-    public function getLambdaClient()
+    public function getLambdaClient(): LambdaClient
     {
         return $this->lambdaClient;
     }
@@ -51,7 +51,7 @@ public function getLambdaClient()
     /**
      * @return CodeDeployClient
      */
-    public function getCodeDeployClient()
+    public function getCodeDeployClient(): CodeDeployClient
     {
         return $this->codeDeployClient;
     }
@@ -59,7 +59,7 @@ public function getCodeDeployClient()
     /**
      * @return array
      */
-    public function getClients()
+    public function getClients(): array
     {
         return [
             $this->s3Client,