diff --git a/tests/src/AddressTransformerTest.php b/tests/src/AddressTransformerTest.php
new file mode 100644
index 0000000..305239e
--- /dev/null
+++ b/tests/src/AddressTransformerTest.php
@@ -0,0 +1,63 @@
+<?php
+/**
+ * Address transformer test
+ *
+ * @author    Pronamic <info@pronamic.eu>
+ * @copyright 2005-2024 Pronamic
+ * @license   GPL-3.0-or-later
+ * @package   Pronamic\WordPress\Pay
+ */
+
+namespace Pronamic\WordPress\Pay\Gateways\Mollie;
+
+use Pronamic\WordPress\Mollie\Address as MollieAddress;
+use Pronamic\WordPress\Pay\Address as PronamicAddress;
+use Pronamic\WordPress\Pay\ContactName;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
+
+/**
+ * Address transformer test class
+ */
+class AddressTransformerTest extends TestCase {
+	/**
+	 * Test transform.
+	 *
+	 * @param string $phone      Phone number.
+	 * @param string $phone_e164 Phone number E164.
+	 *
+	 * @dataProvider transform_provider
+	 */
+	public function test_transform( $phone, $phone_e164 ) {
+		$name = new ContactName();
+
+		$name->set_first_name( 'John' );
+		$name->set_last_name( 'Doe' );
+
+		$pronamic_address = new PronamicAddress();
+
+		$pronamic_address->set_name( $name );
+		$pronamic_address->set_email( 'john.doe@example.com' );
+		$pronamic_address->set_phone( $phone );
+		$pronamic_address->set_line_1( 'Kleine Kerkstraat 1' );
+		$pronamic_address->set_city( 'Leeuwarden' );
+		$pronamic_address->set_country_code( 'NL' );
+
+		$transformer = new AddressTransformer();
+
+		$mollie_address = $transformer->transform_wp_to_mollie( $pronamic_address );
+
+		$this->assertEquals( $phone_e164, $mollie_address->phone );
+	}
+
+	/**
+	 * Transform provider.
+	 *
+	 * @return array
+	 */
+	public function transform_provider() {
+		return [
+			[ '1234567890', '+311234567890' ],
+			[ '+321234567890', '+321234567890' ],
+		];
+	}
+}