diff --git a/tests/DataTransferObject/AbstractDataTransferObjectTest.php b/tests/DataTransferObject/AbstractDataTransferObjectTest.php
new file mode 100644
index 0000000..2f917e6
--- /dev/null
+++ b/tests/DataTransferObject/AbstractDataTransferObjectTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Setono\PeakWMS\DataTransferObject;
+
+use PHPUnit\Framework\TestCase;
+
+final class AbstractDataTransferObjectTest extends TestCase
+{
+    /**
+     * @test
+     */
+    public function it_converts_date_time(): void
+    {
+        $dt = AbstractDataTransferObjectTestDummy::convertDateTime('2024-12-04T12:35:29+02:00');
+
+        self::assertSame('2024-12-04T12:35:29+02:00', $dt->format(\DATE_ATOM));
+    }
+
+    /**
+     * @test
+     */
+    public function it_returns_null_if_input_is_null(): void
+    {
+        $dt = AbstractDataTransferObjectTestDummy::convertDateTime(null);
+
+        self::assertNull($dt);
+    }
+
+    /**
+     * @test
+     */
+    public function it_returns_same_object_if_input_is_date_time(): void
+    {
+        $dt1 = new \DateTimeImmutable('2024-12-04T12:35:29+02:00');
+        $dt2 = AbstractDataTransferObjectTestDummy::convertDateTime($dt1);
+
+        self::assertSame($dt1, $dt2);
+    }
+
+    /**
+     * @test
+     */
+    public function it_returns_date_time_immutable_if_input_is_not(): void
+    {
+        $dt1 = new \DateTime('2024-12-04T12:35:29+02:00');
+        $dt2 = AbstractDataTransferObjectTestDummy::convertDateTime($dt1);
+
+        self::assertSame('2024-12-04T12:35:29+02:00', $dt2->format(\DATE_ATOM));
+    }
+
+    /**
+     * @test
+     */
+    public function it_throws_if_input_cannot_be_converted(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        AbstractDataTransferObjectTestDummy::convertDateTime('2024-12-04T12:35:29.123456+02:00');
+    }
+}
+
+final class AbstractDataTransferObjectTestDummy extends AbstractDataTransferObject
+{
+}