diff --git a/t_operator_test.go b/t_operator_test.go
index e278c95..630be0f 100644
--- a/t_operator_test.go
+++ b/t_operator_test.go
@@ -31,6 +31,8 @@ func TestOperator(t *testing.T) {
 		/*  18 */ {`1^2`, int64(3), nil},
 		/*  19 */ {`3^2`, int64(1), nil},
 		/*  19 */ {`a=1; a^=2`, int64(3), nil},
+		/*  20 */ {`a=1; ++a`, int64(2), nil},
+		/*  21 */ {`a=1; --a`, int64(0), nil},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")