#102 Change SkipLast raises panic if count < 0

skip_last.go

@@ -18,12 +18,16 @@ type skipLastIterator[T any] struct {
 //   itb := gcf.FromSlice([]{1, 2, 3})
 //   itb = gcf.SkipLast(itb, 2)
 //
-// If count is 0 or negative, returns original Iterable.
+// If count is 0, returns original Iterable.
+// If count is negative, raises panic.
 func SkipLast[T any](itb Iterable[T], count int) Iterable[T] {
+	if count < 0 {
+		panic("count for SkipLast must not be negative.")
+	}
 	if isEmpty(itb) {
 		return orEmpty(itb)
 	}
-	if count < 1 {
+	if count == 0 {
 		return itb
 	}
 	return &skipLastIterable[T]{

skip_last_test.go

@@ -14,9 +14,10 @@ func TestSkipLast(t *testing.T) {
 		count int
 	}
 	tests := []struct {
-		name string
-		args args
-		want []int
+		name      string
+		args      args
+		want      []int
+		wantPanic bool
 	}{
 		{
 			name: "skip last 1 from slice 3",
@@ -64,7 +65,7 @@ func TestSkipLast(t *testing.T) {
 				itb:   gcf.FromSlice([]int{1, 2, 3}),
 				count: -1,
 			},
-			want: []int{1, 2, 3},
+			wantPanic: true,
 		},
 		{
 			name: "nil Iterable",
@@ -74,9 +75,23 @@ func TestSkipLast(t *testing.T) {
 			},
 			want: []int{},
 		},
+		{
+			name: "nil and negative",
+			args: args{
+				itb:   nil,
+				count: -1,
+			},
+			wantPanic: true,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
+			if tt.wantPanic {
+				assert.Panics(t, func() {
+					_ = gcf.SkipLast(tt.args.itb, tt.args.count)
+				})
+				return
+			}
 			itb := gcf.SkipLast(tt.args.itb, tt.args.count)
 			s := gcf.ToSlice(itb)
 			assert.Equal(t, tt.want, s)