update stuff

cart-grain_test.go

@@ -39,5 +39,23 @@ func TestAddToCart(t *testing.T) {
 	if grain.TotalPrice != 200 {
 		t.Errorf("Expected total price 200, got %d\n", grain.TotalPrice)
 	}
-
+	if len(grain.Items) != 1 {
+		t.Errorf("Expected 1 item, got %d\n", len(grain.Items))
+	}
+	if grain.Items[0].Quantity != 2 {
+		t.Errorf("Expected quantity 2, got %d\n", grain.Items[0].Quantity)
+	}
+	result, err = grain.HandleMessage(msg, false)
+	if err != nil {
+		t.Errorf("Error handling message: %v\n", err)
+	}
+	if len(result) == 0 {
+		t.Errorf("Expected result, got nil\n")
+	}
+	if grain.Items[0].Quantity != 4 {
+		t.Errorf("Expected quantity 4, got %d\n", grain.Items[0].Quantity)
+	}
+	if grain.TotalPrice != 400 {
+		t.Errorf("Expected total price 400, got %d\n", grain.TotalPrice)
+	}
 }