dbaynard / validity

Validity and validity-based testing

Validity and validity-based testing

Package	Hackage	Stackage
validity
validity-aeson
validity-bytestring
validity-containers
validity-path
validity-primitive
validity-scientific
validity-text
validity-time
validity-unordered-containers
validity-uuid
validity-vector
genvalidity
genvalidity-aeson
genvalidity-bytestring
genvalidity-containers
genvalidity-path
genvalidity-property
genvalidity-scientific
genvalidity-text
genvalidity-time
genvalidity-unordered-containers
genvalidity-uuid
genvalidity-vector
genvalidity-hspec
genvalidity-hspec-aeson
genvalidity-hspec-binary
genvalidity-hspec-cereal
genvalidity-hspec-hashable
genvalidity-hspec-optics

Why?

Make write correct software cheaper.

• Cheap properties
• Free generators
• Free shrinking

Cheap properties

• Property Combinators:

specify "inverse functions" $ inverseFunctions (+1) (-1)
specify "equivalent functions" $ equivalent ((+ 1) . (- 1)) id
specify "transitivity" $ transitivity ((>) :: Int -> Int -> Bool)
specify "symmetry" $ symmetry ((==) :: Int -> Int -> Bool)

• Test suite combinators:

ordSpec @Int

  Ord Int
    (<=) :: Int -> Int -> Bool
      is reflexive for "even Int"'s
        +++ OK, passed 100 tests.
      is antisymmetric for "even Int"'s
        +++ OK, passed 100 tests.
      is transitive for "even Int"'s
        +++ OK, passed 100 tests.
      is equivalent to (\a b -> compare a b /= GT) for "even Int"'s
        +++ OK, passed 100 tests.
    (>=) :: Int -> Int -> Bool
      is reflexive for "even Int"'s
        +++ OK, passed 100 tests.
      is antisymmetric for "even Int"'s
        +++ OK, passed 100 tests.
      is transitive for "even Int"'s
        +++ OK, passed 100 tests.
      is equivalent to (\a b -> compare a b /= LT) for "even Int"'s
        +++ OK, passed 100 tests.
    (<) :: Int -> Int -> Bool
      is antireflexive for "even Int"'s
        +++ OK, passed 100 tests.
      is transitive for "even Int"'s
        +++ OK, passed 100 tests.
      is equivalent to (\a b -> compare a b == LT) for "even Int"'s
        +++ OK, passed 100 tests.
    (>) :: Int -> Int -> Bool
      is antireflexive for "even Int"'s
        +++ OK, passed 100 tests.
      is transitive for "even Int"'s
        +++ OK, passed 100 tests.
      is equivalent to (\a b -> compare a b == GT) for "even Int"'s
        +++ OK, passed 100 tests.

Free generators

data MyType = MyType
  { myRational :: Rational
  , myBool :: Bool
  } deriving (Show, Eq, Generic)

instance Validity MyType -- Implementation is derived via Generic
instance GenUnchecked MyType -- Implementation is derived via Generic
instance GenValid MyType -- Default implementation via GenUnchecked and Validity

genValid :: Gen MyType -- Free access to a generator

Free shrinking

shrinkValid :: MyType -> [MyType] -- Free access to a _valid_ shrinking function

Further Documentation

• Usage example
• Fully worked example
• High-level package overview