Add 2017 reformation day for Germany

Fix #135

src/Cmixin/Holidays/de-national.php

@@ -10,4 +10,5 @@
     'german-unity-day'        => '10-03',
     'christmas'               => '12-25',
     'christmas-next-day'      => '12-26',
+    'reformation-day'         => '= 2017-10-31',
 ];

tests/Cmixin/Holidays/DeTest.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Tests\Cmixin\Holidays;
+
+use Cmixin\BusinessDay;
+use PHPUnit\Framework\TestCase;
+
+class DeTest extends TestCase
+{
+    const CARBON_CLASS = 'Carbon\Carbon';
+
+    protected function setUp(): void
+    {
+        BusinessDay::enable(static::CARBON_CLASS);
+        $carbon = static::CARBON_CLASS;
+        $carbon::resetHolidays();
+    }
+
+    public function testHolidays(): void
+    {
+        $carbon = static::CARBON_CLASS;
+        $carbon::resetHolidays();
+        $carbon::setHolidaysRegion('de-national');
+
+        self::assertFalse($carbon::parse('2024-03-31')->getHolidayName());
+        self::assertFalse($carbon::parse('2024-10-31')->getHolidayName());
+        self::assertSame('Reformation Day', $carbon::parse('2017-10-31')->getHolidayName());
+
+        $carbon::resetHolidays();
+        $carbon::setHolidaysRegion('de-bb');
+
+        self::assertSame('Easter', $carbon::parse('2024-03-31')->getHolidayName());
+    }
+}