diff --git a/tests/Models/AttributeTest.php b/tests/Models/AttributeTest.php
new file mode 100644
index 0000000..c3a950a
--- /dev/null
+++ b/tests/Models/AttributeTest.php
@@ -0,0 +1,72 @@
+<?php
+/**
+ * Jingga
+ *
+ * PHP Version 8.1
+ *
+ * @package   tests
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 2.0
+ * @version   1.0.0
+ * @link      https://jingga.app
+ */
+declare(strict_types=1);
+
+namespace Modules\Admin\tests\Models;
+
+use Modules\Attribute\Models\Attribute;
+
+/**
+ * @testdox Modules\Admin\tests\Models\AttributeTest: Attribute model
+ *
+ * @internal
+ */
+final class AttributeTest extends \PHPUnit\Framework\TestCase
+{
+    public function testDeepClone() : void
+    {
+        $attr = new Attribute();
+
+        $clone = $attr->deepClone();
+
+        $attr->ref = 1;
+
+        self::assertNotEquals($attr->ref, $clone->ref);
+    }
+
+    public function testToArray() : void
+    {
+        $attr = new Attribute();
+
+        $array = $attr->toArray();
+
+        unset($array['type']);
+        unset($array['value']);
+
+        self::assertEquals(
+            [
+                'id' => 0,
+                'ref' => 0,
+            ],
+            $array
+        );
+    }
+
+    public function testJsonSerialize() : void
+    {
+        $attr = new Attribute();
+
+        $array = $attr->jsonSerialize();
+
+        unset($array['type']);
+        unset($array['value']);
+
+        self::assertEquals(
+            [
+                'id' => 0,
+                'ref' => 0,
+            ],
+            $array
+        );
+    }
+}
diff --git a/tests/Models/NullAttributeTest.php b/tests/Models/NullAttributeTest.php
new file mode 100644
index 0000000..ed3748d
--- /dev/null
+++ b/tests/Models/NullAttributeTest.php
@@ -0,0 +1,52 @@
+<?php
+/**
+ * Jingga
+ *
+ * PHP Version 8.1
+ *
+ * @package   tests
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 2.0
+ * @version   1.0.0
+ * @link      https://jingga.app
+ */
+declare(strict_types=1);
+
+namespace Modules\Attribute\tests\Models;
+
+use Modules\Attribute\Models\NullAttribute;
+
+/**
+ * @internal
+ */
+final class NullAttributeTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @covers Modules\Attribute\Models\NullAttribute
+     * @group module
+     */
+    public function testNull() : void
+    {
+        self::assertInstanceOf('\Modules\Attribute\Models\Attribute', new NullAttribute());
+    }
+
+    /**
+     * @covers Modules\Attribute\Models\NullAttribute
+     * @group module
+     */
+    public function testId() : void
+    {
+        $null = new NullAttribute(2);
+        self::assertEquals(2, $null->id);
+    }
+
+    /**
+     * @covers Modules\Attribute\Models\NullAttribute
+     * @group module
+     */
+    public function testJsonSerialize() : void
+    {
+        $null = new NullAttribute(2);
+        self::assertEquals(['id' => 2], $null);
+    }
+}
diff --git a/tests/Models/NullAttributeTypeTest.php b/tests/Models/NullAttributeTypeTest.php
new file mode 100644
index 0000000..173221b
--- /dev/null
+++ b/tests/Models/NullAttributeTypeTest.php
@@ -0,0 +1,52 @@
+<?php
+/**
+ * Jingga
+ *
+ * PHP Version 8.1
+ *
+ * @package   tests
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 2.0
+ * @version   1.0.0
+ * @link      https://jingga.app
+ */
+declare(strict_types=1);
+
+namespace Modules\Attribute\tests\Models;
+
+use Modules\Attribute\Models\NullAttributeType;
+
+/**
+ * @internal
+ */
+final class NullAttributeTypeTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @covers Modules\Attribute\Models\NullAttributeType
+     * @group module
+     */
+    public function testNull() : void
+    {
+        self::assertInstanceOf('\Modules\Attribute\Models\AttributeType', new NullAttributeType());
+    }
+
+    /**
+     * @covers Modules\Attribute\Models\NullAttributeType
+     * @group module
+     */
+    public function testId() : void
+    {
+        $null = new NullAttributeType(2);
+        self::assertEquals(2, $null->id);
+    }
+
+    /**
+     * @covers Modules\Attribute\Models\NullAttributeType
+     * @group module
+     */
+    public function testJsonSerialize() : void
+    {
+        $null = new NullAttributeType(2);
+        self::assertEquals(['id' => 2], $null);
+    }
+}
diff --git a/tests/Models/NullAttributeValueTest.php b/tests/Models/NullAttributeValueTest.php
new file mode 100644
index 0000000..34c1411
--- /dev/null
+++ b/tests/Models/NullAttributeValueTest.php
@@ -0,0 +1,52 @@
+<?php
+/**
+ * Jingga
+ *
+ * PHP Version 8.1
+ *
+ * @package   tests
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 2.0
+ * @version   1.0.0
+ * @link      https://jingga.app
+ */
+declare(strict_types=1);
+
+namespace Modules\Attribute\tests\Models;
+
+use Modules\Attribute\Models\NullAttributeValue;
+
+/**
+ * @internal
+ */
+final class NullAttributeValueTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @covers Modules\Attribute\Models\NullAttributeValue
+     * @group module
+     */
+    public function testNull() : void
+    {
+        self::assertInstanceOf('\Modules\Attribute\Models\AttributeValue', new NullAttributeValue());
+    }
+
+    /**
+     * @covers Modules\Attribute\Models\NullAttributeValue
+     * @group module
+     */
+    public function testId() : void
+    {
+        $null = new NullAttributeValue(2);
+        self::assertEquals(2, $null->id);
+    }
+
+    /**
+     * @covers Modules\Attribute\Models\NullAttributeValue
+     * @group module
+     */
+    public function testJsonSerialize() : void
+    {
+        $null = new NullAttributeValue(2);
+        self::assertEquals(['id' => 2], $null);
+    }
+}