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Agents explore, tests remember

Joel Hooks, October 1, 2026:¶

“run up to 50 agent users using luna:max and have them click through various scenarios. chaos testing. go nuts, fix all the bad stuff”¶

real engineering¶

André Staltz replied:¶

@joelhooks And when those agents find good reproduction steps for a bug, convert that into playwright tests.¶

Agent users click through scenarios and find failures. A good reproduction becomes a repeatable Playwright regression test that repeats the actions and checks their result.¶

rat-stack has yet to build this fifty-agent exploration and Playwright workflow.¶

For executable Effect tests, read tests through supplied services²².¶

Rat-stack’s reading

We connect the proposal to three practices:¶

• Model-based testing¹⁴ generates sequences of actions and checks the system against a model. Agent users can propose action sequences for exploration. Model-based testing¹⁴ also needs a model and assertions.¶
• Property-based testing¹⁸ shrinks a failure to a small counterexample. Keep the smallest useful failing case from exploration, rather than every step the agent happened to take.¶
• The fence³⁹ puts a correction into an enforceable check. A reproduced mistake earns a test when it exposes a genuine behavior gap. Tests that only check the shape of a fix add no such coverage. See tests that earn their place²².¶

A human-driven example

A human-driven signup check found a five-second application-submission timeout and a confirmation email’s /confirm link returning 404. A person found both failures. The resulting checks use Effect tests.¶

Commit 222edd8 raised the timeout to twenty seconds and made timeout request an immediate retry.¶

• The intake test uses TestClock and a hanging fake HTTP client to check the retry outcome.¶
• The route test checks that GET and POST to /confirm return 308. It also checks that the GET redirect preserves the token query.¶

These checks can run without repeating the live check.¶

Last changed 2026-10-07 in e73c9d9. Source on GitHub. Change log.