sum: use DeepEqual to compare

sum/sum_test.go

@@ -1,7 +1,7 @@
 package sum
 
 import (
-	"slices"
+	"reflect"
 	"testing"
 )
 
@@ -21,7 +21,9 @@ func TestSum(t *testing.T) {
 func TestSumAll(t *testing.T) {
 	got := SumAll([]int{1, 2}, []int{0, 9})
 	exp := []int{3, 9}
-	if slices.Compare(got, exp) != 0 {
+
+	// NOTE: check if any two variables are the same
+	if !reflect.DeepEqual(got, exp) {
 		t.Errorf("got %d, expected %d", got, exp)
 	}
 }