mutation fixes

pkg/cart/cart-mutation-helper_test.go

@@ -0,0 +1,68 @@
+package cart
+
+import "testing"
+
+// equalOptional is the nullable-equality primitive shared by the AddItem
+// merge site and any future field-comparison. Two call sites use it today
+// with two distinct types — *uint32 (ParentId) and *string (StoreId) — so
+// the test pins both via generic instantiation.
+func TestEqualOptional(t *testing.T) {
+	t.Run("both nil is equal", func(t *testing.T) {
+		if !equalOptional[string](nil, nil) {
+			t.Error("both nil should be equal")
+		}
+		if !equalOptional[uint32](nil, nil) {
+			t.Error("both nil should be equal (uint32)")
+		}
+	})
+
+	t.Run("same address alias is equal", func(t *testing.T) {
+		s := "x"
+		if !equalOptional(&s, &s) {
+			t.Error("same-address *string should be equal")
+		}
+		v := uint32(5)
+		if !equalOptional(&v, &v) {
+			t.Error("same-address *uint32 should be equal")
+		}
+	})
+
+	t.Run("distinct addresses with equal values are equal", func(t *testing.T) {
+		a, b := "x", "x"
+		if !equalOptional(&a, &b) {
+			t.Error("equal strings at distinct addresses should be equal")
+		}
+		u, w := uint32(5), uint32(5)
+		if !equalOptional(&u, &w) {
+			t.Error("equal uint32 at distinct addresses should be equal")
+		}
+	})
+
+	t.Run("one nil, one set is not equal", func(t *testing.T) {
+		a := "x"
+		if equalOptional(&a, nil) {
+			t.Error("non-nil vs nil should differ (string)")
+		}
+		if equalOptional[string](nil, &a) {
+			t.Error("nil vs non-nil should differ (string)")
+		}
+		u := uint32(5)
+		if equalOptional(&u, nil) {
+			t.Error("non-nil vs nil should differ (uint32)")
+		}
+		if equalOptional[uint32](nil, &u) {
+			t.Error("nil vs non-nil should differ (uint32)")
+		}
+	})
+
+	t.Run("differing values are not equal", func(t *testing.T) {
+		a, b := "x", "y"
+		if equalOptional(&a, &b) {
+			t.Error("differing strings should differ")
+		}
+		u, w := uint32(5), uint32(6)
+		if equalOptional(&u, &w) {
+			t.Error("differing uint32 should differ")
+		}
+	})
+}