At 4:30 PM -0700 8/5/12, Matthew wrote:
On Sun, Aug 5, 2012 at 12:32 AM, Henk-Jan van Tuyl <[email protected]> wrote:
On Sun, 05 Aug 2012 03:21:39 +0200, Matthew <[email protected]> wrote:
I've got a function which takes in two chars, describing a playing
card and a suit. An example would be 4C or TH for a 4 of Clubs or a
Ten of Hearts. I need to be able to compare the ranks of a card (e.g.
a King is 13), so a Card is a tuple of rank and suit. The function
which parses a Card is type String -> Maybe Card.
I'm writing unit tests for this using HUnit, and ideally I'd go with a
table-driven[1] approach, where each test case is a tuple of the input
and the expected output. (Possibly I could expand this to a triple, or
simply a list, to allow for an error message for each test case.) Then
all the test function has to do is run through each case and assert as
necessary. Example: [("TH", Just (Hearts, 10)), ("XH", Nothing)].
A simple solution:
parseCard :: String -> Maybe Card
parseCard string = <your function to test>
test :: Bool
test = all testEqual [("TH", Just (Hearts, 10)), ("XH", Nothing)]
where
testEqual (input, output) = parseCard input == output
For a description of 'all', see:
http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.html#v:all
Thanks for the response. The one problem I have with this is that it
will not be at all obvious which test case (or cases!) failed.
That said, maybe I could do something similar, with a Writer? A passed
test writes "", but a failed one writes a test-specific failure
message. Then the test itself uses this string as the assert message.
Let HUnit tell you about the failing test cases. Here's one way to do it.
import Test.HUnit
import Data.Char (isDigit)
data Suit = Spades | Hearts | Diamonds | Clubs
deriving (Show, Read, Eq, Ord)
type Rank = Int -- 2 .. 14 (jack=11, queen=12, king=13, ace=14)
type Card = (Suit, Rank)
parseCard :: String -> Maybe Card
parseCard [rankChar, suitChar] = do suit <- suitFrom suitChar; rank
<- rankFrom rankChar; return (suit, rank)
parseCard _ = Nothing
suitFrom char = lookup char [('S', Spades), ('H', Hearts), ('D',
Diamonds), ('C', Clubs)]
rankFrom dig | isDigit dig = let v = read [dig] in if v >= 2 then
Just v else Nothing
rankFrom char = lookup char [('T', 10), ('J', 11), ('Q', 12), ('K',
13), ('A', 14)]
makeTest :: (String, Maybe Card) -> Test
makeTest (string, result) = string ~: result ~=? parseCard string
tests = [("TH", Just (Hearts, 10)), ("XH", Nothing)]
main = (runTestTT . TestList . map makeTest) tests
Dean
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