diff --git a/firmware/alu/tests/toy_16.vhd b/firmware/alu/tests/toy_16.vhd
index 3590073..ee0fc1d 100644
--- a/firmware/alu/tests/toy_16.vhd
+++ b/firmware/alu/tests/toy_16.vhd
@@ -133,6 +133,30 @@ begin
         wait for period;
         assert result = "0000101111001001" report "SUB failed";
 
+        info("INC");
+        accu <= "0000000000000000";
+        func <= "1001";
+        wait for period;
+        assert result = "0000000000000001" report "INC failed";
+
+        info("INC-O");
+        accu <= "1111111111111111";
+        func <= "1001";
+        wait for period;
+        assert result = "0000000000000000" report "INC-O failed";
+
+        info("DEC");
+        accu <= "0000000000000001";
+        func <= "1010";
+        wait for period;
+        assert result = "0000000000000000" report "DEC failed";
+
+        info("DEC-O");
+        accu <= "0000000000000000";
+        func <= "1010";
+        wait for period;
+        assert result = "1111111111111111" report "DEC-O failed";
+
         -- terminate test
         wait;