Yup, it's a bit frustrating since it's a problem with LLM, RLHF and fine-tuning for chat. In fact, we also added in the prompt to not say that it did testing. I find that in general it seems really difficult to tell a language model (especially 3.5) to not do something.
The self-review generally catches stuff like this since we tell it that this code is written by an inexperienced developer, so that Sweep becomes more critical.