Coz I have always done coding this way with humans I started out using LLMs to do simple bits of refactoring where tests could be used to validate that the output still worked.
I did not get the impression from this that LLMs were great coders. They would frequently miss stuff, make mistakes and often just ignore the instructions i gave them.
Sometimes they would get it right but not enough. The agentic coding loop still slowed me down overall. Perhaps if i were more junior it would have been a net boost.
Force the LLM to follow a workflow, have it do TDD, use task lists, have it write implementation plans.
LLMs are great coders, but subpar developers, help them be a good developer and you will see massive returns.