Add comprehensive tests for client validation, revenue and expense categories, invoice generation, and schemas

- Implement tests for client validation functions including tax ID, VAT ID, IBAN, BIC, website, and company form validation.
- Create tests for revenue and expense categories ensuring all expected categories and labels are present.
- Add tests for invoice number generation with various scenarios including prefix handling and sequence padding.
- Introduce tests for default categories and their integration, ensuring no overlaps and consistent naming conventions.
- Implement Zod schema validation tests for currency, tax rates, IBAN, tax ID, VAT ID, invoices, companies, and customers.
- Add utility tests for tax calculations, including item amounts and invoice totals, ensuring correct handling of tax rates and formatting.
- Set up Vitest configuration and global test setup for consistent testing environment.

tests/integration/setup.ts

@@ -0,0 +1,128 @@
+import { PrismaClient } from "@prisma/client";
+import { execSync } from "child_process";
+
+/**
+ * Integration Test Setup
+ * Uses a separate test database to avoid polluting development data
+ */
+
+const TEST_DATABASE_URL = process.env.TEST_DATABASE_URL || 
+  "mysql://annas_user:annas_password@localhost:3306/annas_rechnungen_test";
+
+export const testPrisma = new PrismaClient({
+  datasources: {
+    db: {
+      url: TEST_DATABASE_URL,
+    },
+  },
+});
+
+/**
+ * Setup test database: push schema and seed if needed
+ * Returns true if successful, false if database unavailable
+ */
+export async function setupTestDatabase(): Promise<boolean> {
+  console.log("Setting up test database...");
+  
+  try {
+    // Push schema to test database
+    execSync(`npx prisma db push --force-reset`, {
+      env: {
+        ...process.env,
+        DATABASE_URL: TEST_DATABASE_URL,
+      },
+      stdio: "inherit",
+    });
+    
+    console.log("Test database ready");
+    return true;
+  } catch (error) {
+    console.warn("Test database not available:", error);
+    return false;
+  }
+}
+
+/**
+ * Clean up test database
+ */
+export async function cleanupTestDatabase() {
+  // Delete all data in correct order (respecting foreign keys)
+  const tables = [
+    "audit_logs",
+    "invoice_items",
+    "invoices",
+    "buchung_kategorien",
+    "buchungen",
+    "anlagegueter",
+    "services",
+    "customers",
+    "companies",
+    "users",
+  ];
+
+  for (const table of tables) {
+    await testPrisma.$executeRawUnsafe(`DELETE FROM ${table}`);
+  }
+}
+
+/**
+ * Create a test user
+ */
+export async function createTestUser(email: string, username: string) {
+  const bcrypt = await import("bcryptjs");
+  const passwordHash = await bcrypt.default.hash("test1234", 10);
+
+  return testPrisma.user.create({
+    data: {
+      email,
+      username,
+      name: "Test User",
+      passwordHash,
+      role: "ADMIN",
+    },
+  });
+}
+
+/**
+ * Create a test company for a user
+ */
+export async function createTestCompany(userId: string, name: string = "Test GmbH") {
+  return testPrisma.company.create({
+    data: {
+      name,
+      address: "Teststraße 1",
+      zip: "12345",
+      city: "Berlin",
+      country: "DE",
+      userId,
+    },
+  });
+}
+
+/**
+ * Create a test customer for a company
+ */
+export async function createTestCustomer(companyId: string, name: string = "Test Customer") {
+  return testPrisma.customer.create({
+    data: {
+      name,
+      address: "Kundenstraße 1",
+      zip: "54321",
+      city: "Hamburg",
+      country: "DE",
+      companyId,
+    },
+  });
+}
+
+/**
+ * Generate auth cookie for test requests
+ * (Simplified - in real scenario, you'd create a session)
+ */
+export function getAuthHeaders(userId: string) {
+  // For integration tests, we might mock the session or use a test session
+  return {
+    "Content-Type": "application/json",
+    "X-Test-User-Id": userId, // Custom header for test auth bypass
+  };
+}