fix(billing): add defensive check for config.billing.plans and mock config in tests

Author: PierreBrisorgueil

modules/billing/services/billing.webhook.service.js

@@ -13,7 +13,7 @@ const Organization = mongoose.model('Organization');
  * Plan rank lookup — higher index means higher-tier plan.
  * Used to determine upgrade vs downgrade.
  */
-const planRanks = Object.fromEntries(config.billing.plans.map((p, i) => [p, i]));
+const planRanks = Object.fromEntries((config.billing?.plans || []).map((p, i) => [p, i]));
 
 /**
  * @desc Resolve the plan name from a Stripe subscription object.

modules/billing/tests/billing.events.unit.tests.js

@@ -38,6 +38,14 @@ describe('Billing plan.changed event unit tests:', () => {
       },
     }));
 
+    jest.unstable_mockModule('../../../config/index.js', () => ({
+      default: {
+        billing: {
+          plans: ['free', 'starter', 'pro', 'enterprise'],
+        },
+      },
+    }));
+
     // Import service and events from the same module context
     const mod = await import('../services/billing.webhook.service.js');
     BillingWebhookService = mod.default;