fixes

pkg/cart/mutation_add_item_test.go

@@ -0,0 +1,40 @@
+package cart
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	cart_messages "git.k6n.net/go-cart-actor/proto/cart"
+)
+
+// Item identity is the catalog item id, not the (reference-only) SKU: two adds
+// with the same ItemId but different SKU strings must merge into one line.
+func TestAddItem_MergesByItemIdNotSku(t *testing.T) {
+	reg := NewCartMultationRegistry(NewCartMutationContext(nil))
+	g := NewCartGrain(1, time.Now())
+	ctx := context.Background()
+
+	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 144047, Sku: "A0162590", Quantity: 1, Price: 1000}); err != nil {
+		t.Fatalf("first add: %v", err)
+	}
+	// Same id, different (reference) sku string -> should merge, not create a line.
+	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 144047, Sku: "STALE-REF", Quantity: 2, Price: 1000}); err != nil {
+		t.Fatalf("second add: %v", err)
+	}
+
+	if len(g.Items) != 1 {
+		t.Fatalf("items = %d, want 1 (merged by id)", len(g.Items))
+	}
+	if g.Items[0].Quantity != 3 {
+		t.Errorf("quantity = %d, want 3", g.Items[0].Quantity)
+	}
+
+	// A different id is a distinct line.
+	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 170852, Sku: "A0190103", Quantity: 1, Price: 500}); err != nil {
+		t.Fatalf("third add: %v", err)
+	}
+	if len(g.Items) != 2 {
+		t.Fatalf("items = %d, want 2", len(g.Items))
+	}
+}