State transition testing in Testing Fundamentals - Test Execution Trace

Test Overview

This test checks if a simple login system correctly changes states from 'Logged Out' to 'Logged In' and back to 'Logged Out' after logout. It verifies that the system allows login with correct credentials and denies access otherwise.

Test Code - unittest

Testing Fundamentals

class LoginSystem:
    def __init__(self):
        self.state = 'Logged Out'

    def login(self, username, password):
        if username == 'user' and password == 'pass':
            self.state = 'Logged In'
            return True
        else:
            return False

    def logout(self):
        if self.state == 'Logged In':
            self.state = 'Logged Out'
            return True
        return False

import unittest

class TestLoginSystem(unittest.TestCase):
    def setUp(self):
        self.system = LoginSystem()

    def test_valid_login_and_logout(self):
        # Initial state should be Logged Out
        self.assertEqual(self.system.state, 'Logged Out')

        # Login with correct credentials
        login_result = self.system.login('user', 'pass')
        self.assertTrue(login_result)
        self.assertEqual(self.system.state, 'Logged In')

        # Logout should return to Logged Out
        logout_result = self.system.logout()
        self.assertTrue(logout_result)
        self.assertEqual(self.system.state, 'Logged Out')

    def test_invalid_login(self):
        # Attempt login with wrong password
        login_result = self.system.login('user', 'wrong')
        self.assertFalse(login_result)
        self.assertEqual(self.system.state, 'Logged Out')

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

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Test starts and LoginSystem instance is created	System state is 'Logged Out'	Assert initial state is 'Logged Out'	PASS
2	Call login with username 'user' and password 'pass'	System processes login credentials	Assert login returns True and state changes to 'Logged In'	PASS
3	Call logout method	System processes logout	Assert logout returns True and state changes to 'Logged Out'	PASS
4	Call login with username 'user' and wrong password 'wrong'	System processes login credentials	Assert login returns False and state remains 'Logged Out'	PASS

Failure Scenario

Failing Condition: Login method does not change state to 'Logged In' on correct credentials

Execution Trace Quiz - 3 Questions

What is the initial state of the system before any action?

A Logged Out

B Logged In

C Unknown

D Error

Key Result

State transition testing verifies that the system correctly changes from one state to another based on inputs, ensuring all valid and invalid transitions behave as expected.

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