How to test an ATM in a distributed banking system

Problem

How would you test an ATM in a distributed banking system?

Solution
The first thing to do on this question is to clarify assumptions Ask the following questions:

• Who is going to use the ATM? Answers might be “anyone”, or it might be “blind people” – or any number of other answers
• What are they going to use it for? Answers might be “withdrawing money”, “transferring money”, “checking their balance”, or many other answers
• What tools do we have to test? Do we have access to the code, or just the ATM machine?

Remember: a good tester makes sure she knows what she’s testing!
Here are a few test cases for how to test just the withdrawing functionality:

• Withdrawing money less than the account balance
• Withdrawing money greater than the account balance
• Withdrawing money equal to the account balance
• Withdrawing money from an ATM and from the internet at the same time
• Withdrawing money when the connection to the bank’s network is lost
• Withdrawing money from multiple ATMs simultaneously
• Check the balanace avaialble
• Make a deposit at an ATM. 
• Try to enter invalid pin more than 3 times and see if the account gets locked. 
• Try with some grocery card ( an invalid card) whose shape is same as the ATM card, and see what happens 
• Try quick cash with drwal

References
http://tianrunhe.wordpress.com/2012/04/05/how-to-test-an-atm-in-a-distributed-banking-system/