diff --git a/tests/Models/NullDepartmentTest.php b/tests/Models/NullDepartmentTest.php
index 8bd8e89..5db53a9 100755
--- a/tests/Models/NullDepartmentTest.php
+++ b/tests/Models/NullDepartmentTest.php
@@ -47,6 +47,6 @@ final class NullDepartmentTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullDepartment(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullPositionTest.php b/tests/Models/NullPositionTest.php
index 54b0af6..379a8ed 100755
--- a/tests/Models/NullPositionTest.php
+++ b/tests/Models/NullPositionTest.php
@@ -47,6 +47,6 @@ final class NullPositionTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullPosition(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullUnitTest.php b/tests/Models/NullUnitTest.php
index 79773f0..0ded746 100755
--- a/tests/Models/NullUnitTest.php
+++ b/tests/Models/NullUnitTest.php
@@ -47,6 +47,6 @@ final class NullUnitTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullUnit(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }