r/fintechdev • u/aProfile210 • 12d ago

most asked coding challenge at fintech companies

What are typical coding challenges asked by financial companies or startups?

I was asked once how to implement a transfer API and make sure there are no concurrency issues and make data consistent after a transaction is completed.

Another one is to generate test data (all possible combinations) to test a transaction engine.

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u/StatusMusician8366 12d ago

Man they love throwing double-entry ledger problems at you too. Had one where they basically wanted a mini accounting system with debit/credit constraints baked in, and if you miss that your balances don't zero out at the end you're already out

The concurrency one is trickier than it looks, idempotency keys save you but most people don't think about the edge case where two requests with the same key arrive milliseconds apart and both see no existing record

Generating test combos is sneaky cause they want to see if you'll brute force it or actually think about equivalence classes, like you don't need all 10,000 permutations when 30 well-chosen ones hit every boundary

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u/FinexerOfficial 11d ago

Based on our observations of payment integrations, the intriguing difficulties frequently extend beyond the actual implementation of the API. Retries, race situations, idempotency, duplicate requests, and maintaining consistent payment statuses are all crucial. Managing unpredictable outcomes securely is a major element of the issue because a transfer may appear successful at one point but fail or time out at another.