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…

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?