SumAllTails implemented, refactor tests

arrays/sum_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"reflect"
 	"slices"
 	"testing"
 )
@@ -37,3 +38,23 @@ func TestSumAll(t *testing.T) {
 		t.Errorf("got %d want %v", got, want)
 	}
 }
+
+func TestSumAllTails(t *testing.T) {
+	checkSums := func(t testing.TB, got, want []int) {
+		t.Helper()
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("got %v want %v", got, want)
+		}
+	}
+
+	t.Run("sums of slices", func(t *testing.T) {
+		got := SumAllTails([]int{1, 2}, []int{0, 9})
+		want := []int{2, 9}
+		checkSums(t, got, want)
+	})
+	t.Run("sums with some empty slices", func(t *testing.T) {
+		got := SumAllTails([]int{}, []int{3, 4, 5})
+		want := []int{0, 9}
+		checkSums(t, got, want)
+	})
+}