State Transition Testing
State transition testing designs test cases around the different states a system can be in and the valid (and invalid) transitions between them — like an order moving from Pending to Shipped to Delivered — specifically testing that only the allowed transitions can happen and disallowed ones are correctly blocked.
Any system with a meaningful lifecycle — a user account, an order, a subscription, a document approval workflow — has an implicit state machine, whether or not anyone's drawn it out. State transition testing makes that machine explicit and tests it deliberately: every valid transition works, and critically, every invalid transition (cancelling an already-delivered order, for instance) is correctly rejected.
It pairs naturally with a state diagram as the underlying model, and shares DNA with model-based testing — the diagram itself often becomes the direct source that test cases get derived from.
