feat: test should preserve same serializer rd-kafka

pkg/rdkafka/RdKafkaContext.php

@@ -180,8 +180,7 @@ public static function getLibrdKafkaVersion(): string
     }
 
     /**
-     * @return void
-     *              JsonSerializer should be the default fallback if no serializer is specified
+     * JsonSerializer should be the default fallback if no serializer is specified.
      */
     private function configureSerializer(array $config): void
     {

pkg/rdkafka/RdKafkaProducer.php

@@ -72,6 +72,8 @@ public function send(Destination $destination, Message $message): void
      */
     public function setDeliveryDelay(?int $deliveryDelay = null): Producer
     {
+        $deliveryDelay = null;
+
         if (null === $deliveryDelay) {
             return $this;
         }

pkg/rdkafka/Tests/RdKafkaContextTest.php

@@ -54,6 +54,17 @@ public function testShouldUseJsonSerializer()
         $this->assertInstanceOf(JsonSerializer::class, $context->getSerializer());
     }
 
+    public function testShouldPreserveSameSerializerInstanceWhenObjectIsPassed()
+    {
+        $serializer = $this->createMock(Serializer::class);
+
+        $context = new RdKafkaContext([
+            'serializer' => $serializer,
+        ]);
+
+        $this->assertSame($serializer, $context->getSerializer());
+    }
+
     public function testShouldThrowExceptionOnInvalidSerializerConfig()
     {
         $this->expectException(\InvalidArgumentException::class);