Code RoomTransfer tests miss failure modes
MediumPrep Room Coding #4088

Transfer tests miss failure modes

Vibe & agenticAlgorithms & data structuresMid–Senior~15 min

You asked an AI to 'write thorough tests' for a SQL-backed transfer(fromAcct, toAcct, amount) (debits one row, credits another, in a transaction). It generated six tests, all variations of: create two accounts, transfer 100, assert balances are -100 and +100. Everything is green and it claims good coverage. As a reviewer, what's missing, and how would you direct the agent to fill the gaps?

Implement
apply_transfer(balances: list[int], source_index: int, target_index: int, amount: int) → list[int]
Examples
in[[1000,500],0,1,100]out[900,600]
in[[1000,500],0,1,5000]out[1000,500]
in[[1000,500],0,0,100]out[1000,500]
What a strong answer looks like

Treat the AI’s output as a draft to verify, not an answer to trust. Name the specific flaw and the input that triggers it, say how you’d catch it (tests, edge cases, reading critically), and how you’d re-prompt or decompose to get it right.

0:00 of about 15 min

Vibe & agentic: describe the solution in plain language (or narrate it) and the coach grades your approach.

Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.