update tests and discovery

pkg/cart/price_test.go

@@ -133,3 +133,106 @@ func TestPriceMultiplyMethod(t *testing.T) {
 		t.Fatalf("expected exVat %d got %d", exBefore*2, p.ValueExVat())
 	}
 }
+
+func TestGetTaxAmount(t *testing.T) {
+	tests := []struct {
+		total    int64
+		tax      int
+		expected int64
+		desc     string
+	}{
+		{1250, 2500, 250, "25% VAT"}, // 1250 / (1 + 100/25) = 1250 / 5 = 250
+		{1000, 2000, 166, "20% VAT"}, // 1000 / (1 + 100/20) = 1000 / 6 ≈ 166
+		{1200, 2500, 240, "25% VAT on 1200"},
+		{0, 2500, 0, "zero total"},
+		{100, 1000, 9, "10% VAT"},    // tax=1000 for 10%, 100 / (1 + 100/10) = 100 / 11 ≈ 9
+		{100, 10000, 50, "100% VAT"}, // tax=10000 for 100%, 100 / (1 + 100/100) = 100 / 2 = 50
+	}
+
+	for _, tt := range tests {
+		result := GetTaxAmount(tt.total, tt.tax)
+		if result != tt.expected {
+			t.Errorf("GetTaxAmount(%d, %d) [%s] = %d; expected %d", tt.total, tt.tax, tt.desc, result, tt.expected)
+		}
+	}
+}
+
+func TestNewPriceFromIncVatEdgeCases(t *testing.T) {
+	// Zero VAT rate
+	p := NewPriceFromIncVat(1000, 0)
+	if p.IncVat != 1000 {
+		t.Errorf("expected IncVat 1000, got %d", p.IncVat)
+	}
+	if len(p.VatRates) != 1 || p.VatRates[0] != 0 {
+		t.Errorf("expected VAT 0 for rate 0, got %v", p.VatRates)
+	}
+	if p.ValueExVat() != 1000 {
+		t.Errorf("expected exVat 1000, got %d", p.ValueExVat())
+	}
+
+	// High VAT rate, e.g., 50%
+	p = NewPriceFromIncVat(1500, 50)
+	expectedVat := int64(1500 / (1 + 100/50)) // 1500 / 3 = 500
+	if p.VatRates[50] != expectedVat {
+		t.Errorf("expected VAT %d for 50%%, got %d", expectedVat, p.VatRates[50])
+	}
+	if p.ValueExVat() != 1500-expectedVat {
+		t.Errorf("expected exVat %d, got %d", 1500-expectedVat, p.ValueExVat())
+	}
+}
+
+func TestPriceValueExVatAndTotalVat(t *testing.T) {
+	p := Price{IncVat: 13700, VatRates: map[float32]int64{25: 2500, 12: 1200}}
+	exVat := p.ValueExVat()
+	totalVat := p.TotalVat()
+	if exVat != 10000 {
+		t.Errorf("expected exVat 10000, got %d", exVat)
+	}
+	if totalVat != 3700 {
+		t.Errorf("expected totalVat 3700, got %d", totalVat)
+	}
+	if exVat+totalVat != p.IncVat {
+		t.Errorf("exVat + totalVat should equal IncVat: %d + %d != %d", exVat, totalVat, p.IncVat)
+	}
+
+	// Empty VAT rates
+	p2 := Price{IncVat: 500, VatRates: nil}
+	if p2.ValueExVat() != 500 {
+		t.Errorf("expected exVat 500 for no VAT, got %d", p2.ValueExVat())
+	}
+	if p2.TotalVat() != 0 {
+		t.Errorf("expected totalVat 0, got %d", p2.TotalVat())
+	}
+}
+
+func TestMultiplyPriceWithZeroQty(t *testing.T) {
+	base := Price{IncVat: 1250, VatRates: map[float32]int64{25: 250}}
+	multiplied := MultiplyPrice(base, 0)
+	if multiplied.IncVat != 0 {
+		t.Errorf("expected IncVat 0, got %d", multiplied.IncVat)
+	}
+	if len(multiplied.VatRates) != 1 || multiplied.VatRates[25] != 0 {
+		t.Errorf("expected VAT 0, got %v", multiplied.VatRates)
+	}
+}
+
+func TestPriceAddSubtractEdgeCases(t *testing.T) {
+	a := Price{IncVat: 1000, VatRates: map[float32]int64{25: 200}}
+	b := Price{IncVat: 500, VatRates: map[float32]int64{12: 54}} // Different rate
+
+	acc := NewPrice()
+	acc.Add(a)
+	acc.Add(b)
+
+	if acc.VatRates[25] != 200 || acc.VatRates[12] != 54 {
+		t.Errorf("expected VAT 25:200, 12:54, got %v", acc.VatRates)
+	}
+
+	// Subtract more than added (negative VAT)
+	acc.Subtract(a)
+	acc.Subtract(b)
+	acc.Subtract(a) // Subtract extra a
+	if acc.VatRates[25] != -200 || acc.VatRates[12] != 0 {
+		t.Errorf("expected negative VAT for 25 after over-subtract, got %v", acc.VatRates)
+	}
+}