Hi,

   I am trying to use the quickcheck to generate some test-data to test an api, along the lines of http://www.haskell.org/haskellwiki/QuickCheck_as_Test_Set_Generator.

 

For the sake of example, I choose the following function to test

 

 

data Result = Valid | Invalid

api_under_test :: (Int,Int) ->  Result

api_under_test (x,y)
   | (x == 1)  =   Valid
   | otherwise = Invalid 

 

 

I had the following valid-generator which worked quite easily(trivial)

 

validCombinations= [ (1,1), (1,2) ]

validGen = elements validCombinations

prop_valid_api_under_test =
    forAll validGen $ \xs ->
         (api_under_test xs) == (Valid)

 

Now, I want to have a complement to state:

     forall tuples not in validCombinations, the api_under_test must return "Invalid".  (i.e.)

 

prop_invalid_api_under_test =

    forAll invalidGen $ \xs ->

        (api_under_test xs) == (Invalid)
 

 

 

However, inspite of all  googling, and reading the various docs including quickcheck, I am at loss on how I can elegantly define the "invalidGen" generator.  One possible way I can think is to have a customized generator, that would generate two random numbers and then look up the tuple generated against the validCombinations list.

 

However, I feel there just might be a better way of solving this.

 

Any suggestion on how I should be trying to solve this.

 

- Srikanth