feat(billing): renewals, coupons, VAT numbering, billing cycles and invoice payment tracking

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/Feature/CustomBillingCycleTest.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Helpers\OrderHelper;
+use App\Support\BillingCycleCatalog;
+use App\Support\ProductBillingCycles;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class CustomBillingCycleTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_custom_cycle_is_resolved_end_to_end(): void
+    {
+        $this->assertSame([], BillingCycleCatalog::customMonths());
+
+        BillingCycleCatalog::saveCustomMonths([60, 12, 60, 0, 9999]);
+
+        $this->assertSame([60], BillingCycleCatalog::customMonths());
+        $this->assertContains('months_60', BillingCycleCatalog::codes());
+        $this->assertSame(60, OrderHelper::cycleToMonths('months_60'));
+        $this->assertSame('5 năm', BillingCycleCatalog::labelForCode('months_60'));
+        $this->assertContains('months_60', ProductBillingCycles::forType('vps'));
+        $this->assertSame(['annually'], ProductBillingCycles::forType('domain'));
+    }
+
+    public function test_unknown_code_is_rejected(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        OrderHelper::cycleToMonths('months_x');
+    }
+}