Add assertions for phpstan

.github/workflows/phpstan.yml

@@ -36,5 +36,5 @@ jobs:
         with:
           composer-options: "--no-progress --prefer-dist --optimize-autoloader"
 
-      - name: Larastan
+      - name: PHPStan
         run: php ./vendor/bin/phpstan analyse --memory-limit=2G --error-format=github

composer.json

@@ -35,6 +35,8 @@
         }
     },
     "scripts": {
+        "lint": "@phpstan",
+        "phpstan": "@php ./vendor/bin/phpstan analyze",
         "style:check": "@php ./vendor/bin/php-cs-fixer fix --dry-run",
         "style:fix": "@php ./vendor/bin/php-cs-fixer fix"
     }

src/Testing/GivenWhenThen/Scenario.php

@@ -272,12 +272,22 @@ public function usingMessageRepository(InMemoryMessageRepository $messageReposit
 
     public function assertObjectSurvivesSerializationRoundTrip(mixed $input): void
     {
-        $payloadSerializer = $this->payloadSerializer ?? DefaultPayloadSerializer::resolve();
+        if (!isset($this->payloadSerializer)) {
+            $this->payloadSerializer = DefaultPayloadSerializer::resolve();
+        }
+
+        assert(is_object($input), 'Input must be an object.');
 
-        $serializedPayload = $payloadSerializer->serializePayload($input);
+        $serializedPayload = $this->payloadSerializer->serializePayload($input);
         $jsonEncodedSerializedPayload = json_encode($serializedPayload);
+
+        assert(is_string($jsonEncodedSerializedPayload), 'JSON encoding failed.');
+
         $jsonDecodedSerializedPayload = json_decode($jsonEncodedSerializedPayload, true);
-        $unserializedPayload = $payloadSerializer->unserializePayload(get_class($input), $jsonDecodedSerializedPayload);
+
+        assert(is_array($jsonDecodedSerializedPayload), 'JSON decoding failed.');
+
+        $unserializedPayload = $this->payloadSerializer->unserializePayload(get_class($input), $jsonDecodedSerializedPayload);
 
         Assert::assertEquals($input, $unserializedPayload, 'Payload serialization failed round trip.');
     }