Data.GenValidity

GenValidity exists to make tests involving Validity types easier and speed up the generation of data for them.

Let's use the example from Data.Validity again: A datatype that represents primes. To implement tests for this datatype, we would have to be able to generate both primes and non-primes. We could do this with (Prime $ arbitrary) suchThat isValid but this is tedious and inefficient.

The GenValid type class allows you to specify how to (efficiently) generate valid data of the given type to allow for easier and quicker testing. Just instantiating GenUnchecked already gives you access to a default instance of GenValid and GenInvalid but writing custom implementations of these functions may speed up the generation of data.

For example, to generate primes, we don't have to consider even numbers other than 2. A more efficient implementation could then look as follows:

instance GenUnchecked Prime where
    genUnchecked = Prime <$> arbitrary

instance GenValid Prime where
    genValid = Prime <$>
       (oneof
         [ pure 2
         , ((\y -> 2 * abs y + 1) <$> arbitrary) `suchThat` isPrime)
         ])

Typical examples of tests involving validity could look as follows:

it "succeeds when given valid input" $ do
    forAll genValid $ \input ->
        myFunction input `shouldSatisfy` isRight

it "produces valid output when it succeeds" $ do
    forAll genUnchecked $ \input ->
        case myFunction input of
            Nothing -> return () -- Can happen
            Just output -> output `shouldSatisfy` isValid

Documentation

module Data.Validity

class GenUnchecked a where

A class of types for which truly arbitrary values can be generated.

Minimal complete definition

genUnchecked

Methods

genUnchecked :: Gen a

Instances

GenUnchecked Bool

Methods

genUnchecked :: Gen Bool

GenUnchecked Char

Methods

genUnchecked :: Gen Char

GenUnchecked Double

Methods

genUnchecked :: Gen Double

GenUnchecked Float

Methods

genUnchecked :: Gen Float

GenUnchecked Int

Methods

genUnchecked :: Gen Int

GenUnchecked Integer

Methods

genUnchecked :: Gen Integer

GenUnchecked Ordering

Methods

genUnchecked :: Gen Ordering

GenUnchecked Word

Methods

genUnchecked :: Gen Word

GenUnchecked ()

Methods

genUnchecked :: Gen ()

GenUnchecked a => GenUnchecked [a]

Methods

genUnchecked :: Gen [a]

GenUnchecked a => GenUnchecked (Maybe a)

Methods

genUnchecked :: Gen (Maybe a)

(GenUnchecked a, GenUnchecked b) => GenUnchecked (Either a b)

Methods

genUnchecked :: Gen (Either a b)

(GenUnchecked a, GenUnchecked b) => GenUnchecked (a, b)

Methods

genUnchecked :: Gen (a, b)

(GenUnchecked a, GenUnchecked b, GenUnchecked c) => GenUnchecked (a, b, c)

Methods

genUnchecked :: Gen (a, b, c)

class (Validity a, GenUnchecked a) => GenValid a where

A class of types for which valid values can be generated.

If you also write Arbitrary instances for GenValid types, it may be best to simply write arbitrary = genValid.

Methods

genValid :: Gen a

Instances

GenValid Bool

Methods

genValid :: Gen Bool

GenValid Char

Methods

genValid :: Gen Char

GenValid Double

Methods

genValid :: Gen Double

GenValid Float

Methods

genValid :: Gen Float

GenValid Int

Methods

genValid :: Gen Int

GenValid Integer

Methods

genValid :: Gen Integer

GenValid Ordering

Methods

genValid :: Gen Ordering

GenValid Word

Methods

genValid :: Gen Word

GenValid ()

Methods

genValid :: Gen ()

GenValid a => GenValid [a]

If we can generate values of a certain type, we can also generate lists of them.

Methods

genValid :: Gen [a]

GenValid a => GenValid (Maybe a)

Methods

genValid :: Gen (Maybe a)

(GenValid a, GenValid b) => GenValid (Either a b)

Methods

genValid :: Gen (Either a b)

(GenValid a, GenValid b) => GenValid (a, b)

Methods

genValid :: Gen (a, b)

(GenValid a, GenValid b, GenValid c) => GenValid (a, b, c)

Methods

genValid :: Gen (a, b, c)

class (Validity a, GenUnchecked a) => GenInvalid a where

A class of types for which invalid values can be generated.

Methods

genInvalid :: Gen a

Instances

GenInvalid Double

Either NaN or Infinity.

Methods

genInvalid :: Gen Double

GenInvalid Float

Either NaN or Infinity.

Methods

genInvalid :: Gen Float

GenInvalid a => GenInvalid [a]

This instance ensures that the generated list contains at least one element that satisfies isInvalid. The rest is unchecked.

Methods

genInvalid :: Gen [a]

GenInvalid a => GenInvalid (Maybe a)

Methods

genInvalid :: Gen (Maybe a)

(GenInvalid a, GenInvalid b) => GenInvalid (Either a b)

This instance ensures that the generated tupse contains at least one invalid element. The other element is unchecked.

Methods

genInvalid :: Gen (Either a b)

(GenInvalid a, GenInvalid b) => GenInvalid (a, b)

Methods

genInvalid :: Gen (a, b)

(GenInvalid a, GenInvalid b, GenInvalid c) => GenInvalid (a, b, c)

This instance ensures that the generated triple contains at least one invalid element. The other two are unchecked.

Methods

genInvalid :: Gen (a, b, c)

upTo :: Int -> Gen Int

upTo generates an integer between 0 (inclusive) and n.

genSplit :: Int -> Gen (Int, Int)

'genSplit a' generates a tuple '(b, c)' such that 'b + c' equals a.

genSplit3 :: Int -> Gen (Int, Int, Int)

'genSplit a' generates a triple '(b, c, d)' such that 'b + c + d' equals a.

arbPartition :: Int -> Gen [Int]

'arbPartition n' generates a list ls such that 'sum ls' equals n.

genListOf :: Gen a -> Gen [a]

A version of listOf that takes size into account more accurately.