AnnasRechnungsManager/tests/lib/tax.test.ts

import {
  TAX_RATES,
  calcItemAmounts,
  calcItemAmountsKleinunternehmer,
  calcInvoiceTotals,
  formatCurrency,
  formatDate,
} from "@/lib/tax";

describe("tax.ts - German Tax Calculations", () => {
  describe("TAX_RATES", () => {
    it("should have correct tax rate values", () => {
      expect(TAX_RATES).toEqual([
        { label: "19% MwSt. (Regelsteuersatz)", value: 19 },
        { label: "7% MwSt. (ermäßigt)", value: 7 },
        { label: "0% (steuerfrei / §13b UStG)", value: 0 },
      ]);
    });
  });

  describe("calcItemAmounts", () => {
    it("should calculate correct amounts for 19% tax", () => {
      const result = calcItemAmounts(2, 100, 19);
      expect(result).toEqual({
        netAmount: 200,
        taxAmount: 38,
        grossAmount: 238,
      });
    });

    it("should calculate correct amounts for 7% tax", () => {
      const result = calcItemAmounts(1, 50, 7);
      expect(result).toEqual({
        netAmount: 50,
        taxAmount: 3.5,
        grossAmount: 53.5,
      });
    });

    it("should handle tax-free items (0%)", () => {
      const result = calcItemAmounts(3, 33.33, 0);
      expect(result).toEqual({
        netAmount: 99.99,
        taxAmount: 0,
        grossAmount: 99.99,
      });
    });

    it("should handle decimal quantities", () => {
      const result = calcItemAmounts(1.5, 100, 19);
      expect(result).toEqual({
        netAmount: 150,
        taxAmount: 28.5,
        grossAmount: 178.5,
      });
    });

    it("should round to 2 decimal places", () => {
      const result = calcItemAmounts(1, 33.333, 19);
      // 33.333 * 19% = 6.333..., rounded to 6.33
      expect(result.netAmount).toBe(33.33);
      expect(result.taxAmount).toBe(6.33);
      expect(result.grossAmount).toBe(39.66);
    });
  });

  describe("calcItemAmountsKleinunternehmer", () => {
    it("should set tax to 0 for Kleinunternehmer", () => {
      const result = calcItemAmountsKleinunternehmer(2, 100);
      expect(result).toEqual({
        netAmount: 200,
        taxAmount: 0,
        grossAmount: 200,
      });
    });

    it("should treat gross as net for Kleinunternehmer", () => {
      const result = calcItemAmountsKleinunternehmer(1, 50);
      expect(result.netAmount).toBe(50);
      expect(result.grossAmount).toBe(50);
    });
  });

  describe("calcInvoiceTotals", () => {
    it("should sum up multiple invoice items", () => {
      const items = [
        { netAmount: 100, taxAmount: 19, grossAmount: 119 },
        { netAmount: 50, taxAmount: 3.5, grossAmount: 53.5 },
      ];
      const result = calcInvoiceTotals(items);
      expect(result).toEqual({
        netTotal: 150,
        taxTotal: 22.5,
        grossTotal: 172.5,
      });
    });

    it("should handle empty items array", () => {
      const result = calcInvoiceTotals([]);
      expect(result).toEqual({
        netTotal: 0,
        taxTotal: 0,
        grossTotal: 0,
      });
    });

    it("should round totals to 2 decimal places", () => {
      const items = [
        { netAmount: 33.333, taxAmount: 6.333, grossAmount: 39.666 },
        { netAmount: 66.666, taxAmount: 12.666, grossAmount: 79.332 },
      ];
      const result = calcInvoiceTotals(items);
      // calcInvoiceTotals uses Math.round which rounds 99.999 to 100
      expect(result.netTotal).toBe(100);
      expect(result.taxTotal).toBe(19);
      expect(result.grossTotal).toBe(119);
    });

    it("should handle Kleinunternehmer invoice (no tax)", () => {
      const items = [
        { netAmount: 100, taxAmount: 0, grossAmount: 100 },
        { netAmount: 200, taxAmount: 0, grossAmount: 200 },
      ];
      const result = calcInvoiceTotals(items);
      expect(result).toEqual({
        netTotal: 300,
        taxTotal: 0,
        grossTotal: 300,
      });
    });
  });

  describe("formatCurrency", () => {
    it("should format number to EUR currency", () => {
      // Note: Intl.NumberFormat uses non-breaking space (\u00A0) before €
      expect(formatCurrency(1234.56)).toBe("1.234,56\u00A0€");
    });

    it("should handle string input", () => {
      expect(formatCurrency("999.99")).toBe("999,99\u00A0€");
    });

    it("should format zero correctly", () => {
      expect(formatCurrency(0)).toBe("0,00\u00A0€");
    });
  });

  describe("formatDate", () => {
    it("should format Date object to German format", () => {
      const date = new Date("2026-05-08");
      expect(formatDate(date)).toBe("8.5.2026");
    });

    it("should format date string to German format", () => {
      expect(formatDate("2026-12-31")).toBe("31.12.2026");
    });
  });
});