Not trying to be snarky, with all due respect... this is a skill issue.

It's a tool. It's a wildly effective and capable tool. I don't know how or why I have such a wildly different experience than so many that describe their experiences in a similar manner... but... nearly every time I come to the same conclusion that the input determines the output.

> If they implement something with a not-so-great approach, they'll keep adding workarounds or redundant code every time they run into limitations later.

Yes, when the prompt/instructions are overly broad and there's no set of guardrails or guidelines that indicate how things should be done... this will happen. If you're not using planning mode, skill issue. You have to get all this stuff wrapped up and sorted before the implementation begins. If the implementation ends up being done in a "not-so-great" approach - that's on you.

> If you tell them the code is slow

Whew. Ok. You don't tell it the code is slow. Do you tell your coworker "Hey, your code is slow" and expect great results? You ask it to benchmark the code and then you ask it how it might be optimized. Then you discuss those options with it (this is where you do the part from the previous paragraph, where you direct the approach so it doesn't do "no-so-great approach") until you get to a point where you like the approach and the model has shown it understands what's going on.

Then you accept the plan and let the model start work. At this point you should have essentially directed the approach and ensured that it's not doing anything stupid. It will then just execute, it'll stay within the parameters/bounds of the plan you established (unless you take it off the rails with a bunch of open ended feedback like telling it that it's buggy instead of being specific about bugs and how you expect them to be resolved).

> you can have 10 bespoke tests for every bug. Plus a new mocking framework created every time the last one turns out to be unfit for purpose.

This is an area I will agree that the models are wildly inept. Someone needs to study what it is about tests and testing environments and mocking things that just makes these things go off the rails. The solution to this is the same as the solution to the issue of it keeping digging or chasing it's tail in circles... Early in the prompt/conversation/message that sets the approach/intent/task you state your expectations for the final result. Define the output early, then describe/provide context/etc. The earlier in the prompt/conversation the "requirements" are set the more sticky they'll be.

And this is exactly the same for the tests. Either write your own tests and have the models build the feature from the test or have the model build the tests first as part of the planned output and then fill in the functionality from the pre-defined test. Be very specific about how your testing system/environment is setup and any time you run into an issue testing related have the model make a note about that and the solution in a TESTING.md document. In your AGENTS.md or CLAUDE.md or whatever indicate that if the model is working with tests it should refer to the TESTING.md document for notes about the testing setup.

Personally, I focus on the functionality, get things integrated and working to the point I'm ready to push it to a staging or production (yolo) environment and _then_ have the model analyze that working system/solution/feature/whatever and write tests. Generally my notes on the testing environment to the model are something along the lines of a paragraph describing the basic testing flow/process/framework in use and how I'd like things to work.

The more you stick to convention the better off you'll be. And use planning mode.

LLMs work best when the user defines their acceptance criteria first