The validation logic had been solid for months. Pydantic schema on the request, a service-layer check for the actual business rule, tests green across the board. Then I added a CLI tool that talked to the same API the web app used, and within a week a support ticket came in: a record existed in...
Source: [Dev.to](https://dev.to/den0011/one-api-three-clients-and-the-validation-rule-that-only-one-of-them-obeyed-47b3)