State transition testing in Testing Fundamentals - Build an Automation Script

Verify state transitions of a simple turnstile

Preconditions (1)

Step 1: Check that the turnstile is Locked

Step 2: Insert a coin

Step 3: Verify the turnstile changes to Unlocked state

Step 4: Push the turnstile

Step 5: Verify the turnstile changes back to Locked state

Step 6: Push the turnstile again

Step 7: Verify the turnstile remains Locked

Step 8: Insert a coin again

Step 9: Verify the turnstile changes to Unlocked state

✅ Expected Result: The turnstile correctly changes states according to the inputs: Locked -> Unlocked after coin, Unlocked -> Locked after push, Locked remains Locked after push without coin

Automation Requirements - unittest

Assertions Needed:

Assert initial state is Locked

Assert state changes to Unlocked after coin

Assert state changes to Locked after push

Assert state remains Locked after push without coin

Best Practices:

Use a State Machine class to represent states and transitions

Use clear method names for actions (insert_coin, push)

Use unittest assertions for validation

Keep tests independent and clear

Automated Solution

Testing Fundamentals

import unittest

class Turnstile:
    def __init__(self):
        self.state = 'Locked'

    def insert_coin(self):
        if self.state == 'Locked':
            self.state = 'Unlocked'

    def push(self):
        if self.state == 'Unlocked':
            self.state = 'Locked'

class TestTurnstileStateTransitions(unittest.TestCase):
    def setUp(self):
        self.turnstile = Turnstile()

    def test_state_transitions(self):
        # Initial state
        self.assertEqual(self.turnstile.state, 'Locked')

        # Insert coin unlocks
        self.turnstile.insert_coin()
        self.assertEqual(self.turnstile.state, 'Unlocked')

        # Push locks again
        self.turnstile.push()
        self.assertEqual(self.turnstile.state, 'Locked')

        # Push again stays locked
        self.turnstile.push()
        self.assertEqual(self.turnstile.state, 'Locked')

        # Insert coin unlocks again
        self.turnstile.insert_coin()
        self.assertEqual(self.turnstile.state, 'Unlocked')

if __name__ == '__main__':
    unittest.main()

This test uses a simple Turnstile class to model the states Locked and Unlocked.

The insert_coin method changes the state from Locked to Unlocked only.

The push method changes the state from Unlocked to Locked only.

The test case test_state_transitions checks the initial state, then simulates inserting a coin and pushing the turnstile, verifying the state changes after each action.

Assertions confirm the state is exactly as expected after each step, ensuring the state machine behaves correctly.

Common Mistakes - 3 Pitfalls

Not initializing the state before testing

Changing state incorrectly on invalid actions

Using print statements instead of assertions

Bonus Challenge

Now add data-driven testing with 3 different sequences of actions and expected final states

Show Hint

Practice

1. What is the main purpose of state transition testing in software testing?

easy

A. To check how the system behaves when moving from one state to another

B. To test the speed of the software under load

C. To verify the user interface design

D. To check the installation process of the software

Solution

1. Step 1: Understand the concept of state transition testing

   State transition testing focuses on how software changes from one state to another based on events or inputs.

2. Step 2: Match the purpose with the options

   To check how the system behaves when moving from one state to another correctly describes checking system behavior during state changes, which is the core of state transition testing.

3. Final Answer:

   To check how the system behaves when moving from one state to another -> Option A

4. Quick Check:

   State transition testing = check state changes [OK]

Hint: Focus on system behavior during state changes [OK]

Common Mistakes:

• Confusing state transition testing with performance testing
• Thinking it tests UI design
• Mixing it with installation testing

2. Which of the following is the correct way to represent a state transition in a test case?

easy

A. State A --(event)--> State B

B. State A + State B = Event

C. Event = State A and State B

D. State A * Event = State B

Solution

1. Step 1: Recall the notation for state transitions

   State transitions are usually shown as one state moving to another state triggered by an event, written as State A --(event)--> State B.

2. Step 2: Compare with given options

   State A --(event)--> State B matches the standard notation. Other options use incorrect symbols or formats.

3. Final Answer:

   State A --(event)--> State B -> Option A

4. Quick Check:

   Correct notation = State A --(event)--> State B [OK]

Hint: Look for arrow with event in parentheses [OK]

Common Mistakes:

• Using incorrect symbols like + or *
• Confusing event placement
• Mixing states and events in wrong order

3. Consider a system with states: Locked and Unlocked. The event InsertCoin moves it from Locked to Unlocked. What is the next state after InsertCoin if the system is currently Locked?

medium

A. Locked

B. Unlocked

C. Error

D. Unknown

Solution

1. Step 1: Identify current state and event

   The system is currently in the Locked state, and the event InsertCoin occurs.

2. Step 2: Apply the state transition rule

   According to the rule, InsertCoin moves the system from Locked to Unlocked state.

3. Final Answer:

   Unlocked -> Option B

4. Quick Check:

   Locked + InsertCoin = Unlocked [OK]

Hint: Follow event rules from current state [OK]

Common Mistakes:

• Assuming state stays the same after event
• Choosing error or unknown without reason
• Ignoring the given transition rule

4. A tester wrote a state transition test but missed the event that moves the system from Idle to Active. What is the likely problem in the test?

medium

A. The test will check UI elements incorrectly

B. The test will run faster

C. The test will cause a syntax error

D. The test will not cover all possible state changes

Solution

1. Step 1: Understand the missing event impact

   Missing the event means the test does not check the transition from Idle to Active state.

2. Step 2: Identify the consequence on test coverage

   Without this event, the test misses a possible state change, reducing coverage and possibly missing bugs.

3. Final Answer:

   The test will not cover all possible state changes -> Option D

4. Quick Check:

   Missing event = incomplete state coverage [OK]

Hint: Check all events for full coverage [OK]

Common Mistakes:

• Thinking missing event causes syntax error
• Assuming test speed changes
• Confusing state transitions with UI checks

5. You have a vending machine with states: Idle, HasMoney, and Dispensing. Events are InsertCoin, SelectItem, and DispenseItem. Which test case best checks the transition from HasMoney to Dispensing?

hard

A. Start in Idle, SelectItem, then InsertCoin

B. Start in Dispensing, InsertCoin, then SelectItem

C. Start in Idle, InsertCoin, then SelectItem

D. Start in HasMoney, DispenseItem, then InsertCoin

Solution

1. Step 1: Identify the transition from HasMoney to Dispensing

   The event that moves the machine from HasMoney to Dispensing is SelectItem.

2. Step 2: Find the test case that triggers this transition

   Start in Idle, InsertCoin, then SelectItem starts Idle, InsertCoin (moves to HasMoney), then SelectItem (moves to Dispensing), correctly testing the transition.

3. Final Answer:

   Start in Idle, InsertCoin, then SelectItem -> Option C

4. Quick Check:

   HasMoney + SelectItem = Dispensing [OK]

Hint: Trace events to reach target transition [OK]

Common Mistakes:

• Starting in wrong state
• Using events in wrong order
• Ignoring correct event for transition