Tests pass, users furious: DavidKPiano calls for 'behavioral diff' tests in the agent era
DavidKPiano · x · 2026-10-24
Developer DavidKPiano (David Khourshid) highlights a new failure mode of agentic development: an app can be fully tested yet still feel broken. His four-step scenario: 1) ship UI/UX version A, fully tested; 2) users get used to A; 3) an agent rewrites the UI to version B and rewrites the tests to match, indifferent to A; 4) users expect A but get B. Traditional tests only verify code–test consistency, not changes to established user-facing behavior — so he argues the industry needs a new kind of "behavioral diff" test to catch agents breaking user expectations.
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