diff --git a/tests/Models/NullStockLocationTest.php b/tests/Models/NullStockLocationTest.php
index 3cd3625..cb2ca90 100644
--- a/tests/Models/NullStockLocationTest.php
+++ b/tests/Models/NullStockLocationTest.php
@@ -47,6 +47,6 @@ final class NullStockLocationTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullStockLocation(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullStockShelfTest.php b/tests/Models/NullStockShelfTest.php
index 686a75c..19cf483 100644
--- a/tests/Models/NullStockShelfTest.php
+++ b/tests/Models/NullStockShelfTest.php
@@ -47,6 +47,6 @@ final class NullStockShelfTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullStockShelf(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullStockTest.php b/tests/Models/NullStockTest.php
index 6a14091..17dac74 100644
--- a/tests/Models/NullStockTest.php
+++ b/tests/Models/NullStockTest.php
@@ -47,6 +47,6 @@ final class NullStockTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullStock(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }