Test the same value if it already exist in property

src/DtoTest.php

@@ -96,11 +96,11 @@ private function assetMappings(SortedMap $getterSetterMapping, $instance): void
 
                 $this->callGetter($fieldName, $pair->getter(), $instance, $newObject);
             } elseif ($pair->isImmutable()) {
-                $newObject = $this->createObject($fieldName, (string) $pair->getter()->getReturnType());
-                ReflectionClass::createFromInstance($instance)
-                    ->getProperty($fieldName)
-                    ->setValue($instance, $newObject)
-                ;
+                $reflectionProperty = ReflectionClass::createFromInstance($instance)->getProperty($fieldName);
+                if (($newObject = $reflectionProperty->getValue($instance)) === null) {
+                    $newObject = $this->createObject($fieldName, (string) $pair->getter()->getReturnType());
+                    $reflectionProperty->setValue($instance, $newObject);
+                }
 
                 $this->callGetter($fieldName, $pair->getter(), $instance, $newObject);
             }

tests/PHPUnit/Constructor.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPUnit;
+
+class Constructor
+{
+    /** @var string */
+    private $string;
+
+    /** @var int */
+    private $int;
+
+    /** @var bool */
+    private $bool;
+
+    public function __construct(string $string, int $int, bool $bool)
+    {
+        $this->string = $string;
+        $this->int = $int;
+        $this->bool = $bool;
+    }
+
+    public function string(): string
+    {
+        return $this->string;
+    }
+
+    public function int(): int
+    {
+        return $this->int;
+    }
+
+    public function isBool(): bool
+    {
+        return $this->bool;
+    }
+}

tests/PHPUnit/ContructorTest.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPUnit;
+
+use DtoTester\DtoTest;
+
+class ContructorTest extends DtoTest
+{
+    protected function getInstance()
+    {
+        return new Constructor('string', 42, false);
+    }
+}