QuickCheck-2.14.3: Automatic testing of Haskell programs
Safe HaskellSafe
LanguageHaskell2010

Test.QuickCheck.Monadic

Description

Allows testing of monadic values. Will generally follow this form:

prop_monadic a b = monadicIO $ do
  a' <- run (f a)
  b' <- run (f b)
  -- ...
  assert someBoolean

Example using the FACTOR(1) command-line utility:

import System.Process
import Test.QuickCheck
import Test.QuickCheck.Monadic

-- $ factor 16
-- 16: 2 2 2 2
factor :: Integer -> IO [Integer]
factor n = parse `fmap` readProcess "factor" [show n] "" where

  parse :: String -> [Integer]
  parse = map read . tail . words

prop_factor :: Positive Integer -> Property
prop_factor (Positive n) = monadicIO $ do
  factors <- run (factor n)

  assert (product factors == n)

>>> quickCheck prop_factor
+++ OK, passed 100 tests.

See the paper "Testing Monadic Code with QuickCheck".

Synopsis

Property monad

newtype PropertyM (m :: Type -> Type) a Source #

The property monad is really a monad transformer that can contain monadic computations in the monad m it is parameterized by:

  • m - the m-computations that may be performed within PropertyM

Elements of PropertyM m a may mix property operations and m-computations.

Constructors

MkPropertyM 

Fields

Instances

Instances details
MonadTrans PropertyM Source # 
Instance details

Defined in Test.QuickCheck.Monadic

Methods

lift :: Monad m => m a -> PropertyM m a #

Monad m => MonadFail (PropertyM m) Source # 
Instance details

Defined in Test.QuickCheck.Monadic

Methods

fail :: String -> PropertyM m a #

MonadIO m => MonadIO (PropertyM m) Source # 
Instance details

Defined in Test.QuickCheck.Monadic

Methods

liftIO :: IO a -> PropertyM m a #

Applicative (PropertyM m) Source # 
Instance details

Defined in Test.QuickCheck.Monadic

Methods

pure :: a -> PropertyM m a #

(<*>) :: PropertyM m (a -> b) -> PropertyM m a -> PropertyM m b #

liftA2 :: (a -> b -> c) -> PropertyM m a -> PropertyM m b -> PropertyM m c #

(*>) :: PropertyM m a -> PropertyM m b -> PropertyM m b #

(<*) :: PropertyM m a -> PropertyM m b -> PropertyM m a #

Functor (PropertyM m) Source # 
Instance details

Defined in Test.QuickCheck.Monadic

Methods

fmap :: (a -> b) -> PropertyM m a -> PropertyM m b #

(<$) :: a -> PropertyM m b -> PropertyM m a #

Monad m => Monad (PropertyM m) Source # 
Instance details

Defined in Test.QuickCheck.Monadic

Methods

(>>=) :: PropertyM m a -> (a -> PropertyM m b) -> PropertyM m b #

(>>) :: PropertyM m a -> PropertyM m b -> PropertyM m b #

return :: a -> PropertyM m a #

Monadic specification combinators

run :: Monad m => m a -> PropertyM m a Source #

The lifting operation of the property monad. Allows embedding monadic/IO-actions in properties:

log :: Int -> IO ()

prop_foo n = monadicIO $ do
  run (log n)
  -- ...

assert :: forall (m :: Type -> Type). Monad m => Bool -> PropertyM m () Source #

Allows embedding non-monadic properties into monadic ones.

assertWith :: forall (m :: Type -> Type). Monad m => Bool -> String -> PropertyM m () Source #

Like assert but allows caller to specify an explicit message to show on failure.

Example:

do
  assertWith True  "My first predicate."
  assertWith False "My other predicate."
  ...

Assertion failed (after 2 tests):
    Passed: My first predicate
    Failed: My other predicate

pre :: forall (m :: Type -> Type). Monad m => Bool -> PropertyM m () Source #

Tests preconditions. Unlike assert this does not cause the property to fail, rather it discards them just like using the implication combinator ==>.

This allows representing the Hoare triple

{p} x ← e{q}

as

pre p
x <- run e
assert q

wp :: Monad m => m a -> (a -> PropertyM m b) -> PropertyM m b Source #

The weakest precondition

wp(x ← e, p)

can be expressed as in code as wp e (\x -> p).

pick :: forall (m :: Type -> Type) a. (Monad m, Show a) => Gen a -> PropertyM m a Source #

Quantification in a monadic property, fits better with do-notation than forAllM. Note: values generated by pick do not shrink.

forAllM :: forall (m :: Type -> Type) a b. (Monad m, Show a) => Gen a -> (a -> PropertyM m b) -> PropertyM m b Source #

Quantification in monadic properties to pick, with a notation similar to forAll. Note: values generated by forAllM do not shrink.

monitor :: forall (m :: Type -> Type). Monad m => (Property -> Property) -> PropertyM m () Source #

Allows making observations about the test data:

monitor (collect e)

collects the distribution of value of e.

monitor (counterexample "Failure!")

Adds "Failure!" to the counterexamples.

stop :: forall prop (m :: Type -> Type) a. (Testable prop, Monad m) => prop -> PropertyM m a Source #

Run functions

monadic :: (Testable a, Monad m) => (m Property -> Property) -> PropertyM m a -> Property Source #

monadic' :: (Testable a, Monad m) => PropertyM m a -> Gen (m Property) Source #

monadicIO :: Testable a => PropertyM IO a -> Property Source #

Runs the property monad for IO-computations.

prop_cat msg = monadicIO $ do
  (exitCode, stdout, _) <- run (readProcessWithExitCode "cat" [] msg)

  pre (ExitSuccess == exitCode)

  assert (stdout == msg)

>>> quickCheck prop_cat
+++ OK, passed 100 tests.

monadicST :: Testable a => (forall s. PropertyM (ST s) a) -> Property Source #

Runs the property monad for ST-computations.

-- Your mutable sorting algorithm here
sortST :: Ord a => [a] -> ST s (MVector s a)
sortST = thaw . fromList . sort

prop_sortST xs = monadicST $ do
  sorted  <- run (freeze =<< sortST xs)
  assert (toList sorted == sort xs)

>>> quickCheck prop_sortST
+++ OK, passed 100 tests.

runSTGen :: (forall s. Gen (ST s a)) -> Gen a Source #