iSQI Exam CTFL_Syll2018 Topic 1 Question 41 Discussion

You need to test a vending machine for light drinks The machine has a button for each of the drinks it contains

Pressing a button before inserting coins, will display the cost of the drink

Pressing the same button after inserting enough coins will dispense the drink and provide change if needed)

If the machine is out of the specific drink, and the button for this drink is pressed, the machine displays "Sold Out" (regardless if coins were inserted or not).

Which test technique is most suitable for this situation?