Agentic Engineering Patterns - Simon Willison's Weblog

Simon Willison’s Weblog

We're going to do it again, aren't we? We're going to take something simple and sensible ("write tests first", "small composable modules", etc.), give it a fancy complicated name ("Behavior-Constrained Implementation Lifecycle pattern", "Boundary-Scoped Processing Constructs pattern", etc.), and create an entire industry of consultants and experts selling books and enterprise coaching around it, each swearing they have the secret sauce and the right incantations.

The damn thing _talks_. You can just _speak_ to it. You can just ask it to do what you want.

Wait: "write tests first" isn't simple and it's controversial. The benefits of TDD in pure-human development are debatable (I'd argue, in many cases, even dubious). But the equation changes with LLMs, because the cost of generating tests (and of keeping them up to date) plummets, and test cases are some of the easiest code to generate and reason about.

It's not as simple an observation as you're making it out to be.