Examples
Also called Specification by example, Few-shot prompting
Showing what you want with concrete inputs and the results they must give, in place of or beside a description. A good one settles what a paragraph leaves open, and it is hard to read two ways.
Examples are direct, but most of them rule out very little. "Jan 15 gives Feb 15" leaves wrong programs standing that "Jan 31 gives Feb 28" removes at once. The useful ones sit at the edges, so you have to know where the edges are.
Say it to your agent
“nextBillingDate must do this: Jan 15 plus 1 gives Feb 15. Jan 31 plus 1 gives Feb 28. Jan 31 plus 2 gives Mar 31, not Mar 28. Feb 29 2024 plus 12 gives Feb 28 2025. Write these as tests first.”