Test setting, then resetting a custom serializer:

my_object.to_string(standard)={ "abc": 12, "foo": "bar" }

my_object.to_string(custom serializer)=Custom Output

Next line of output should be from the custom freeit function:

freeit, value=123

my_object.to_string(standard)={ "abc": 12, "foo": "bar" }

Check that the custom serializer isn't free'd until the last json_object_put:

my_object.to_string(custom serializer)=Custom Output

Next line of output should be from the custom freeit function:

freeit, value=123