diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1fa9609..a3fe8d3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,7 +27,7 @@ jobs:
     steps:
       - uses: zenstruck/.github@php-cs-fixer
         with:
-          php: 8
+          php: 8.1
           key: ${{ secrets.GPG_PRIVATE_KEY }}
           token: ${{ secrets.COMPOSER_TOKEN }}
 
diff --git a/tests/DependencyInjection/ZenstruckScheduleExtensionTest.php b/tests/DependencyInjection/ZenstruckScheduleExtensionTest.php
index 78c587c..ba52de5 100644
--- a/tests/DependencyInjection/ZenstruckScheduleExtensionTest.php
+++ b/tests/DependencyInjection/ZenstruckScheduleExtensionTest.php
@@ -14,6 +14,7 @@
 use Matthias\SymfonyDependencyInjectionTest\PhpUnit\AbstractExtensionTestCase;
 use Symfony\Component\Config\Definition\Exception\InvalidConfigurationException;
 use Symfony\Component\DependencyInjection\Argument\TaggedIteratorArgument;
+use Symfony\Component\DependencyInjection\Reference;
 use Zenstruck\ScheduleBundle\Command\ScheduleListCommand;
 use Zenstruck\ScheduleBundle\Command\ScheduleRunCommand;
 use Zenstruck\ScheduleBundle\DependencyInjection\ZenstruckScheduleExtension;
@@ -134,7 +135,7 @@ public function can_configure_single_server_lock_factory()
     {
         $this->load(['single_server_lock_factory' => 'my_factory']);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(SingleServerHandler::class, 0, 'my_factory');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(SingleServerHandler::class, 0, new Reference('my_factory'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(SingleServerHandler::class, 'schedule.extension_handler');
     }
 
@@ -145,7 +146,7 @@ public function can_configure_without_overlapping_handler_lock_factory()
     {
         $this->load(['without_overlapping_lock_factory' => 'my_factory']);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(WithoutOverlappingHandler::class, 0, 'my_factory');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(WithoutOverlappingHandler::class, 0, new Reference('my_factory'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(WithoutOverlappingHandler::class, 'schedule.extension_handler');
     }
 
@@ -156,9 +157,9 @@ public function can_configure_http_client()
     {
         $this->load(['http_client' => 'my_client']);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(PingHandler::class, 0, 'my_client');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(PingHandler::class, 0, new Reference('my_client'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(PingHandler::class, 'schedule.extension_handler');
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(PingTaskRunner::class, 0, 'my_client');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(PingTaskRunner::class, 0, new Reference('my_client'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(PingTaskRunner::class, 'schedule.task_runner');
     }
 
@@ -169,7 +170,7 @@ public function can_enable_messenger_with_default_bus(): void
     {
         $this->load(['messenger' => null]);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(MessageTaskRunner::class, 0, 'message_bus');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(MessageTaskRunner::class, 0, new Reference('message_bus'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(MessageTaskRunner::class, 'schedule.task_runner');
     }
 
@@ -180,7 +181,7 @@ public function can_enable_messenger_with_custom_bus(): void
     {
         $this->load(['messenger' => ['message_bus' => 'my_bus']]);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(MessageTaskRunner::class, 0, 'my_bus');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(MessageTaskRunner::class, 0, new Reference('my_bus'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(MessageTaskRunner::class, 'schedule.task_runner');
     }
 
@@ -196,7 +197,7 @@ public function can_configure_email_handler()
             'subject_prefix' => '[Acme Inc]',
         ]]);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 0, 'my_mailer');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 0, new Reference('my_mailer'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(EmailHandler::class, 'schedule.extension_handler');
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 1, 'from@example.com');
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 2, 'to@example.com');
@@ -216,7 +217,7 @@ public function can_configure_notifier_handler()
             'subject_prefix' => '[Acme Inc]',
         ]]);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 0, 'my_notifier');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 0, new Reference('my_notifier'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(NotifierHandler::class, 'schedule.extension_handler');
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 1, ['chat/slack']);
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 2, 'to@example.com');
@@ -237,7 +238,7 @@ public function can_configure_notifier_handler_with_array_channel()
             'subject_prefix' => '[Acme Inc]',
         ]]);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 0, 'my_notifier');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 0, new Reference('my_notifier'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(NotifierHandler::class, 'schedule.extension_handler');
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 1, ['chat/slack', 'teams']);
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 2, 'to@example.com');
@@ -254,7 +255,7 @@ public function minimum_email_handler_configuration()
             'service' => 'my_mailer',
         ]]);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 0, 'my_mailer');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 0, new Reference('my_mailer'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(EmailHandler::class, 'schedule.extension_handler');
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 1, null);
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(EmailHandler::class, 2, null);
@@ -270,7 +271,7 @@ public function minimum_notifier_handler_configuration()
             'service' => 'my_notifier',
         ]]);
 
-        $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 0, 'my_notifier');
+        $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 0, new Reference('my_notifier'));
         $this->assertContainerBuilderHasServiceDefinitionWithTag(NotifierHandler::class, 'schedule.extension_handler');
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 1, []);
         $this->assertContainerBuilderHasServiceDefinitionWithArgument(NotifierHandler::class, 2, null);
diff --git a/tests/Schedule/Task/Runner/ProcessTaskRunnerTest.php b/tests/Schedule/Task/Runner/ProcessTaskRunnerTest.php
index b37f69c..a4d5791 100644
--- a/tests/Schedule/Task/Runner/ProcessTaskRunnerTest.php
+++ b/tests/Schedule/Task/Runner/ProcessTaskRunnerTest.php
@@ -41,7 +41,8 @@ public function can_create_failed_result()
 
         $this->assertTrue($result->isFailure());
         $this->assertSame('Exit 127: Command not found', $result->getDescription());
-        $this->assertSame("sh: 1: sdfsdfsdf: not found\n", $result->getOutput());
+        $this->assertStringContainsString('sdfsdfsdf', $result->getOutput());
+        $this->assertStringContainsString('not found', $result->getOutput());
     }
 
     /**