Validate birth date

tests/PHPUnit/WcGateway/Helper/PayUponInvoiceHelperTest.php

@@ -0,0 +1,32 @@
+<?php
+declare(strict_types=1);
+
+namespace WooCommerce\PayPalCommerce\WcGateway\Helper;
+
+use DateTime;
+use WooCommerce\PayPalCommerce\TestCase;
+
+class PayUponInvoiceHelperTest extends TestCase
+{
+	/**
+	 * @dataProvider datesProvider
+	 */
+	public function testValidateBirthDate($input, $output)
+	{
+		$this->assertSame((new PayUponInvoiceHelper())->validate_birth_date($input), $output);
+	}
+
+	public function datesProvider(): array{
+		$format = 'Y-m-d';
+
+		return [
+			['', false],
+			[(new DateTime())->format($format), false],
+			[(new DateTime('-17 years'))->format($format), false],
+			['31-02-1942', false],
+			['01-01-1942', false],
+			['1942-01-01', true],
+		];
+	}
+
+}