My implementation of Guy Royse's Vending Machine Kata.

Vending machines are really just Finite State Machines and can be implemented in hardware. If the wikipedia article above is a bit too heavy, there's a great video from Computerphile, Computers without memory.

Being we're building a state machine, I suspect we'll make use of the state pattern.

The following display states exist:

1. No Money (Insert Coin/Exact Change)
2. Money (Current Value)
3. Display Price
4. Display Thank you!
5. Sold Out

• The change making algorithm does find opitmal results, but the Exact Change Only algorithm does not.
  • Move to the Greedy Algorithm to make it a more robust solution all around.
• I don't care for the fact that the abstract base VendingMachineState class has knowledge of its inheritors.
  • It was implemented this way to centralize logic that would have otherwise had to have been implemented in each of the child classes.
  • Find a way to decouple it.
• There are several missing states. A few of the states have if...then logic that should really be represented as different states unto themselves.

Nothing special here. Just compile and run the tests.