In the prior two chapters I talked about how to test functions and the like with properties via proper and quickcheck. This chapter will expore the idea of how to test a developing system with property based testing.
In this case we are going to take a look at a the betting system of a poker game for two players. We want to look at how we handle betting, we are not going to focus on making sure that the shuffle of the cards is really random. nor on determining a winner at showdown.
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Note
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I am assuming a heads up game of limit Texas-Holdem, if you are not familar with poker then don’t worry, it won’t affect your understanding of the chapter much. You can find the rules on the web if you want. |
In this game we have two players, the dealer and the big blind, in the start state the dealer has put out 1 credit, and the big blind 2 and each player has two cards.
The players take turns acting, at any given point a player has several possible actions, he can fold which will end the game and cause the other player to win, he can bet which will push the action back to the other player or he can call which is to say that he matches the other player’s bet, and this will end the round. (We are going to ignore the option of checking and all in bets for now).
After each round more cards are delt. and a new round of betting happens. In the first round the dealer goes first, in the other rounds the big blind goes first. There are four rounds of betting, initial, flop , turn and river. At the end of the river. At the end of the river round if no player has folded then the game procedes to a showdown. Where the player with the best hand will win, (or if players have equivilent hands they will split the pot.) This chapter will not concern the determining winner at showdown, only that it happens or not.
This gives us a FINITE state machine that looks like this
image::images/pker_fsm.jpg #TODO Redraw image without "all in" lines
While we can (and probably should) write tests for each transition in the FSM it would also be useful to have a set of tests that we can run on the system as a whole to test the properties of the game as a system.