State transition testing is a type of testing that the system that is tested by transitioning between its different states and verifying that the correct behavior is exhibited for each state transition. This testing ensures that the system behaves correctly as it moves from one state to another. To perform state transition testing we would create test cases to cover all possible state transitions and ensure that the system behaves correctly for each transition.
Let’s consider an example of state transition testing for a simple traffic light system with three states: Red, Yellow, and Green.
Here are the states and the events that cause transitions between them:
Red: The traffic light is red, and the traffic is stopped.
Green: The traffic light is green, and the traffic is moving.
Yellow: The traffic light is yellow, and the traffic is preparing to stop.
The events that cause transitions between the states are:
Red to Green: When the timer for the red light expires, the traffic light switches to green.
Green to Yellow: After a certain period, the traffic light switches to yellow to signal the traffic to prepare to stop.
Yellow to Red: After a certain period, the traffic light switches to red, and the traffic stops.
Here are some examples of test cases:
Verify that when the system starts, the traffic light is in the red state, and the traffic is stopped.
Verify that when the timer for the red light expires, the traffic light switches to green, and the traffic starts moving.
Verify that after a certain period, the traffic light switches from green to yellow to signal the traffic to prepare to stop.
Verify that after a certain period, the traffic light switches from yellow to red, and the traffic stops.
Verify that if the timer for the red light expires while the traffic light is already in the green state, the system behaves correctly and transitions to the yellow state before switching to red.
These test cases ensure that the traffic light system behaves correctly for all possible state transitions and helps identify any defects related to state changes and transitions.