Re: [Haskell-cafe] HUnit and table-driven tests

On Sun, Aug 5, 2012 at 12:32 AM, Henk-Jan van Tuyl wrote:

On Sun, 05 Aug 2012 03:21:39 +0200, Matthew 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.htm...

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.

Regards, Henk-Jan van Tuyl

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