Refine Slice read error test

parser_test.go

@@ -53,8 +53,7 @@ func TestSlice(t *testing.T) {
 	}))
 	t.Run("fails when read fails", rapid.MakeCheck(func(t *rapid.T) {
 		expectedErr := rapid.Map(rapid.StringN(0, 100, -1), errors.New).Draw(t, "err")
-		r := ptest.ErrReaderAt(expectedErr)
-		c := cursor.NewReaderAt(r)
+		c := ptest.ErrCursor[byte](expectedErr)
 		s := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "s")
 		result, err := gigaparsec.Slice(s)(gigaparsec.MakeState(c))
 		failed, _, _ := result.Failed()