"add tests and do some tweaks" there's the snake in the grass - you're asking the LLM to write tests after the code is generated, so naturally, it will write p

"add tests and do some tweaks" there's the snake in the grass - you're asking the LLM to write tests after the code is generated, so naturally, it will write passing tests - including tests which enforce buggy behavior if not now, then you're lucky; watch out for next time.