How well do agents use test/verification techniques?
Conventional wisdom says you can improve agent output quality by telling them to use TDD, property-based testing, or formal verification — but does it actually work? This blog post systematically tests 26 different testing instructions (from 'use QuickCheck' to 'use Lean 4' to 'make no mistakes') on coding agents implementing Zstd in Rust, measuring real correctness outcomes. The results challenge the assumption that naively prompting agents with testing buzzwords meaningfully improves correctness, and give practitioners a concrete, empirical basis for deciding which testing guidance is actually worth including in their agent prompts.
Takeaways3
- Simply telling an agent to 'use TDD' or 'use property-based testing' does not reliably improve implementation correctness.
- Some formal verification and fuzzing techniques do show measurable benefit, but results vary significantly by tool and task.
- The gap between what testing techniques sound good and what actually moves the needle for agents is large — empirical testing of your prompts matters.










































































