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

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