State transition happens when a system changes it's state due to some reasons.
1. Some advertisements are going on ATM machine. As soon as user enters and ATM card, advertisements are stopped and it askes for a PIN
2. Use clicks a send button and email is sent
In test data definition, one may use state transition for defining test data for testing. I hope it is clear now
State transition testing uses the same principles as the State Transition Diagramming design technique. State transition testing focuses on the testing of transitions from one state (e.g., open, closed) of an object (e.g., an account) to another state. Incorporate the state transition testing preparation into the test scenario building process. For example, include tests of an account transitioning from open to closed and an account transitioning from closed to open (e.g., account closed in error).
State transition testing is used where some aspect of the system can be described in what is called a 'finite state machine'. This simply means that the system can be in a (finite) number of different states, and the transitions from one state to another are determined by the rules of the 'machine.
Any system where you get a different output for the same input, depending on what has happened before, is a finite state system. A finite state system is often shown as a state diagram
A system may exhibit a different response depending on current conditions or previous history (its state). In this case, that aspect of the system can be shown as a state transition diagram. It allows the tester to view the software in terms of its states, transitions between states, the inputs or events that trigger state changes (transitions) and the actions which may result from those transitions. The states of the system or object under test are separate, identifiable and finite in number.
A state transition model has four basic parts:
• the states that the software may occupy (open/closed or funded/insufficient funds);
• the transitions from one state to another (not all transitions are allowed);
• the events that cause a transition (closing a file or withdrawing money);
• the actions that result from a transition (an error message or being given your cash).
Note that in any given state, one event can cause only one action, but that the same event - from a different state - may cause a different action and a dif-ferent end state