QuickCheck-2.7.3: Automatic testing of Haskell programs

Safe Haskell | Safe
Language | Haskell98

Test.QuickCheck

Contents

- Running tests
  - Running tests verbosely
  - Testing all properties in a module
  - Testing polymorphic properties
- Random generation
  - Generator combinators
  - Generators which use Arbitrary
  - Running a generator
  - Generator debugging
- Arbitrary and CoArbitrary classes
  - Helper functions for implementing arbitrary
  - Helper functions for implementing shrink
  - Helper functions for implementing coarbitrary
  - Type-level modifiers for changing generator behavior
- Properties
  - Property combinators
    - Controlling property execution
    - Conjunction and disjunction
    - What to do on failure
    - Analysing test distribution
    - Miscellaneous

Synopsis

- quickCheck :: Testable prop => prop -> IO ()
- data Args = Args {
  - replay :: Maybe (QCGen, Int)
  - maxSuccess :: Int
  - maxDiscardRatio :: Int
  - maxSize :: Int
  - chatty :: Bool
  }
- data Result
  - = Success {
    - numTests :: Int
    - labels :: [(String, Int)]
    - output :: String
    }
  - | GaveUp {
    - numTests :: Int
    - labels :: [(String, Int)]
    - output :: String
    }
  - | Failure {
    - numTests :: Int
    - numShrinks :: Int
    - numShrinkTries :: Int
    - numShrinkFinal :: Int
    - usedSeed :: QCGen
    - usedSize :: Int
    - reason :: String
    - theException :: Maybe AnException
    - labels :: [(String, Int)]
    - output :: String
    }
  - | NoExpectedFailure {
    - numTests :: Int
    - labels :: [(String, Int)]
    - output :: String
    }
- stdArgs :: Args
- quickCheckWith :: Testable prop => Args -> prop -> IO ()
- quickCheckWithResult :: Testable prop => Args -> prop -> IO Result
- quickCheckResult :: Testable prop => prop -> IO Result
- verboseCheck :: Testable prop => prop -> IO ()
- verboseCheckWith :: Testable prop => Args -> prop -> IO ()
- verboseCheckWithResult :: Testable prop => Args -> prop -> IO Result
- verboseCheckResult :: Testable prop => prop -> IO Result
- quickCheckAll :: Q Exp
- verboseCheckAll :: Q Exp
- forAllProperties :: Q Exp
- polyQuickCheck :: Name -> ExpQ
- polyVerboseCheck :: Name -> ExpQ
- monomorphic :: Name -> ExpQ
- data Gen a
- choose :: Random a => (a, a) -> Gen a
- oneof :: [Gen a] -> Gen a
- frequency :: [(Int, Gen a)] -> Gen a
- elements :: [a] -> Gen a
- growingElements :: [a] -> Gen a
- sized :: (Int -> Gen a) -> Gen a
- resize :: Int -> Gen a -> Gen a
- suchThat :: Gen a -> (a -> Bool) -> Gen a
- suchThatMaybe :: Gen a -> (a -> Bool) -> Gen (Maybe a)
- listOf :: Gen a -> Gen [a]
- listOf1 :: Gen a -> Gen [a]
- vectorOf :: Int -> Gen a -> Gen [a]
- infiniteListOf :: Gen a -> Gen [a]
- vector :: Arbitrary a => Int -> Gen [a]
- orderedList :: (Ord a, Arbitrary a) => Gen [a]
- infiniteList :: Arbitrary a => Gen [a]
- generate :: Gen a -> IO a
- sample :: Show a => Gen a -> IO ()
- sample' :: Gen a -> IO [a]
- class Arbitrary a where
  - arbitrary :: Gen a
  - shrink :: a -> [a]
- class CoArbitrary a where
  - coarbitrary :: a -> Gen b -> Gen b
- arbitrarySizedIntegral :: Integral a => Gen a
- arbitrarySizedFractional :: Fractional a => Gen a
- arbitrarySizedBoundedIntegral :: (Bounded a, Integral a) => Gen a
- arbitraryBoundedIntegral :: (Bounded a, Integral a) => Gen a
- arbitraryBoundedRandom :: (Bounded a, Random a) => Gen a
- arbitraryBoundedEnum :: (Bounded a, Enum a) => Gen a
- genericShrink :: (Generic a, Typeable a, RecursivelyShrink (Rep a), Subterms (Rep a)) => a -> [a]
- subterms :: (Generic a, Typeable a, Subterms (Rep a)) => a -> [a]
- recursivelyShrink :: (Generic a, RecursivelyShrink (Rep a)) => a -> [a]
- shrinkNothing :: a -> [a]
- shrinkList :: (a -> [a]) -> [a] -> [[a]]
- shrinkIntegral :: Integral a => a -> [a]
- shrinkRealFrac :: RealFrac a => a -> [a]
- shrinkRealFracToInteger :: RealFrac a => a -> [a]
- variant :: Integral n => n -> Gen a -> Gen a
- coarbitraryIntegral :: Integral a => a -> Gen b -> Gen b
- coarbitraryReal :: Real a => a -> Gen b -> Gen b
- coarbitraryShow :: Show a => a -> Gen b -> Gen b
- coarbitraryEnum :: Enum a => a -> Gen b -> Gen b
- (><) :: (Gen a -> Gen a) -> (Gen a -> Gen a) -> Gen a -> Gen a
- newtype Blind a = Blind {
  - getBlind :: a
  }
- newtype Fixed a = Fixed {
  - getFixed :: a
  }
- newtype OrderedList a = Ordered {
  - getOrdered :: [a]
  }
- newtype NonEmptyList a = NonEmpty {
  - getNonEmpty :: [a]
  }
- newtype Positive a = Positive {
  - getPositive :: a
  }
- newtype NonZero a = NonZero {
  - getNonZero :: a
  }
- newtype NonNegative a = NonNegative {
  - getNonNegative :: a
  }
- newtype Large a = Large {
  - getLarge :: a
  }
- newtype Small a = Small {
  - getSmall :: a
  }
- data Smart a = Smart Int a
- newtype Shrink2 a = Shrink2 {
  - getShrink2 :: a
  }
- data Shrinking s a = Shrinking s a
- class ShrinkState s a where
  - shrinkInit :: a -> s
  - shrinkState :: a -> s -> [(a, s)]
- data Property
- class Testable prop where
  - property :: prop -> Property
  - exhaustive :: prop -> Bool
- forAll :: (Show a, Testable prop) => Gen a -> (a -> prop) -> Property
- forAllShrink :: (Show a, Testable prop) => Gen a -> (a -> [a]) -> (a -> prop) -> Property
- shrinking :: Testable prop => (a -> [a]) -> a -> (a -> prop) -> Property
- (==>) :: Testable prop => Bool -> prop -> Property
- (===) :: (Eq a, Show a) => a -> a -> Property
- ioProperty :: Testable prop => IO prop -> Property
- verbose :: Testable prop => prop -> Property
- once :: Testable prop => prop -> Property
- within :: Testable prop => Int -> prop -> Property
- noShrinking :: Testable prop => prop -> Property
- (.&.) :: (Testable prop1, Testable prop2) => prop1 -> prop2 -> Property
- (.&&.) :: (Testable prop1, Testable prop2) => prop1 -> prop2 -> Property
- conjoin :: Testable prop => [prop] -> Property
- (.||.) :: (Testable prop1, Testable prop2) => prop1 -> prop2 -> Property
- disjoin :: Testable prop => [prop] -> Property
- counterexample :: Testable prop => String -> prop -> Property
- printTestCase :: Testable prop => String -> prop -> Property
- whenFail :: Testable prop => IO () -> prop -> Property
- whenFail' :: Testable prop => IO () -> prop -> Property
- expectFailure :: Testable prop => prop -> Property
- label :: Testable prop => String -> prop -> Property
- collect :: (Show a, Testable prop) => a -> prop -> Property
- classify :: Testable prop => Bool -> String -> prop -> Property
- cover :: Testable prop => Bool -> Int -> String -> prop -> Property
- data Discard = Discard
- discard :: a
- mapSize :: Testable prop => (Int -> Int) -> prop -> Property

# Running tests

quickCheck :: Testable prop => prop -> IO ()

Tests a property and prints the results to `stdout`.

data Args

Args specifies arguments to the QuickCheck driver

Constructors

Args |
Fields replay :: Maybe (QCGen, Int) Should we replay a previous test? maxSuccess :: Int Maximum number of successful tests before succeeding maxDiscardRatio :: Int Maximum number of discarded tests per successful test before giving up maxSize :: Int Size to use for the biggest test cases chatty :: Bool Whether to print anything

Instances

Read Args |
Show Args |

data Result

Result represents the test result

Constructors

Success | A successful test run
Fields numTests :: Int Number of tests performed labels :: [(String, Int)] Labels and frequencies found during all successful tests output :: String Printed output
GaveUp | Given up
Fields numTests :: Int Number of tests performed labels :: [(String, Int)] Labels and frequencies found during all successful tests output :: String Printed output
Failure | A failed test run
Fields numTests :: Int Number of tests performed numShrinks :: Int Number of successful shrinking steps performed numShrinkTries :: Int Number of unsuccessful shrinking steps performed numShrinkFinal :: Int Number of unsuccessful shrinking steps performed since last successful shrink usedSeed :: QCGen What seed was used usedSize :: Int What was the test size reason :: String Why did the property fail theException :: Maybe AnException The exception the property threw, if any labels :: [(String, Int)] Labels and frequencies found during all successful tests output :: String Printed output
NoExpectedFailure | A property that should have failed did not
Fields numTests :: Int Number of tests performed labels :: [(String, Int)] Labels and frequencies found during all successful tests output :: String Printed output

Instances

Show Result |

stdArgs :: Args

The default test arguments

quickCheckWith :: Testable prop => Args -> prop -> IO ()

Tests a property, using test arguments, and prints the results to `stdout`.

quickCheckWithResult :: Testable prop => Args -> prop -> IO Result

Tests a property, using test arguments, produces a test result, and prints the results to `stdout`.

quickCheckResult :: Testable prop => prop -> IO Result

Tests a property, produces a test result, and prints the results to `stdout`.

## Running tests verbosely

verboseCheck :: Testable prop => prop -> IO ()

Tests a property and prints the results and all test cases generated to `stdout`. This is just a convenience function that means the same as ``quickCheck` . `verbose``.

verboseCheckWith :: Testable prop => Args -> prop -> IO ()

Tests a property, using test arguments, and prints the results and all test cases generated to `stdout`. This is just a convenience function that combines `quickCheckWith` and `verbose`.

verboseCheckWithResult :: Testable prop => Args -> prop -> IO Result

Tests a property, using test arguments, produces a test result, and prints the results and all test cases generated to `stdout`. This is just a convenience function that combines `quickCheckWithResult` and `verbose`.

verboseCheckResult :: Testable prop => prop -> IO Result

Tests a property, produces a test result, and prints the results and all test cases generated to `stdout`. This is just a convenience function that combines `quickCheckResult` and `verbose`.

## Testing all properties in a module

quickCheckAll :: Q Exp

Test all properties in the current module. The name of the property must begin with `prop_`. Polymorphic properties will be defaulted to `Integer`. Returns `True` if all tests succeeded, `False` otherwise.

Using `quickCheckAll` interactively doesn't work. Instead, add a definition to your module along the lines of

    runTests = $quickCheckAll

and then execute `runTests`.

verboseCheckAll :: Q Exp

Test all properties in the current module. This is just a convenience function that combines `quickCheckAll` and `verbose`.

forAllProperties :: Q Exp

Test all properties in the current module, using a custom `quickCheck` function. The same caveats as with `quickCheckAll` apply.

`$`forAllProperties`` has type `(`Property` -> `IO` `Result`) -> `IO` `Bool``. An example invocation is `$`forAllProperties` `quickCheckResult``, which does the same thing as `$`quickCheckAll``.

## Testing polymorphic properties

polyQuickCheck :: Name -> ExpQ

Test a polymorphic property, defaulting all type variables to `Integer`.

Invoke as `$(`polyQuickCheck` 'prop)`, where `prop` is a property. Note that just evaluating ``quickCheck` prop` in GHCi will seem to work, but will silently default all type variables to `()`!

`$(`polyQuickCheck` 'prop)` means the same as ``quickCheck` $(`monomorphic` 'prop)`. If you want to supply custom arguments to `polyQuickCheck`, you will have to combine `quickCheckWith` and `monomorphic` yourself.

polyVerboseCheck :: Name -> ExpQ

Test a polymorphic property, defaulting all type variables to `Integer`. This is just a convenience function that combines `verboseCheck` and `monomorphic`.

monomorphic :: Name -> ExpQ

Monomorphise an arbitrary property by defaulting all type variables to `Integer`.

For example, if `f` has type ``Ord` a => [a] -> [a]` then `$(`monomorphic` 'f)` has type `[`Integer`] -> [`Integer`]`.

# Random generation

data Gen a

A generator for values of type `a`.

Instances

Monad Gen |
Functor Gen |
Applicative Gen |
Testable prop => Testable (Gen prop) |

## Generator combinators

choose :: Random a => (a, a) -> Gen a

Generates a random element in the given inclusive range.

oneof :: [Gen a] -> Gen a

Randomly uses one of the given generators. The input list must be non-empty.

frequency :: [(Int, Gen a)] -> Gen a

Chooses one of the given generators, with a weighted random distribution. The input list must be non-empty.

elements :: [a] -> Gen a

Generates one of the given values. The input list must be non-empty.

growingElements :: [a] -> Gen a

Takes a list of elements of increasing size, and chooses among an initial segment of the list. The size of this initial segment increases with the size parameter. The input list must be non-empty.

sized :: (Int -> Gen a) -> Gen a

Used to construct generators that depend on the size parameter.

resize :: Int -> Gen a -> Gen a

Overrides the size parameter. Returns a generator which uses the given size instead of the runtime-size parameter.

suchThat :: Gen a -> (a -> Bool) -> Gen a

Generates a value that satisfies a predicate.

suchThatMaybe :: Gen a -> (a -> Bool) -> Gen (Maybe a)

Tries to generate a value that satisfies a predicate.

listOf :: Gen a -> Gen [a]

Generates a list of random length. The maximum length depends on the size parameter.

listOf1 :: Gen a -> Gen [a]

Generates a non-empty list of random length. The maximum length depends on the size parameter.

vectorOf :: Int -> Gen a -> Gen [a]

Generates a list of the given length.

infiniteListOf :: Gen a -> Gen [a]

Generates an infinite list.

## Generators which use Arbitrary

vector :: Arbitrary a => Int -> Gen [a]

Generates a list of a given length.

orderedList :: (Ord a, Arbitrary a) => Gen [a]

Generates an ordered list of a given length.

infiniteList :: Arbitrary a => Gen [a]

Generate an infinite list.

## Running a generator

generate :: Gen a -> IO a

Run a generator.

## Generator debugging

sample :: Show a => Gen a -> IO ()

Generates some example values and prints them to `stdout`.

sample' :: Gen a -> IO [a]

Generates some example values.

# Arbitrary and CoArbitrary classes

class Arbitrary a where

Random generation and shrinking of values.

Minimal complete definition

Nothing

Methods

arbitrary :: Gen a

A generator for values of the given type.

shrink :: a -> [a]

Produces a (possibly) empty list of all the possible immediate shrinks of the given value. The default implementation returns the empty list, so will not try to shrink the value.

Most implementations of `shrink` should try at least three things:

1. Shrink a term to any of its immediate subterms.
2. Recursively apply `shrink` to all immediate subterms.
3. Type-specific shrinkings such as replacing a constructor by a simpler constructor.

For example, suppose we have the following implementation of binary trees:

    data Tree a = Nil | Branch a (Tree a) (Tree a)

We can then define `shrink` as follows:

    shrink Nil = []
    shrink (Branch x l r) =
      -- shrink Branch to Nil
      [Nil] ++
      -- shrink to subterms
      [l, r] ++
      -- recursively shrink subterms
      [Branch x' l' r' | (x', l', r') <- shrink (x, l, r)]

There are a couple of subtleties here:

- QuickCheck tries the shrinking candidates in the order they appear in the list, so we put more aggressive shrinking steps (such as replacing the whole tree by `Nil`) before smaller ones (such as recursively shrinking the subtrees).
- It is tempting to write the last line as `[Branch x' l' r' | x' <- shrink x, l' <- shrink l, r' <- shrink r]` but this is the wrong thing! It will force QuickCheck to shrink `x`, `l` and `r` in tandem, and shrinking will stop once one of the three is fully shrunk.

There is a fair bit of boilerplate in the code above. We can avoid it with the help of some generic functions; note that these only work on GHC 7.2 and above. The function `genericShrink` tries shrinking a term to all of its subterms and, failing that, recursively shrinks the subterms. Using it, we can define `shrink` as:

    shrink x = shrinkToNil x ++ genericShrink x
      where
        shrinkToNil Nil = []
        shrinkToNil (Branch _ l r) = [Nil]

`genericShrink` is a combination of `subterms`, which shrinks a term to any of its subterms, and `recursivelyShrink`, which shrinks all subterms of a term. These may be useful if you need a bit more control over shrinking than `genericShrink` gives you.

A final gotcha: we cannot define `shrink` as simply ``shrink` x = Nil:`genericShrink` x` as this shrinks `Nil` to `Nil`, and shrinking will go into an infinite loop.

If all this leaves you bewildered, you might try ``shrink` = `genericShrink`` to begin with, after deriving `Generic` and `Typeable` for your type. However, if your data type has any special invariants, you will need to check that `genericShrink` can't break those invariants.

Instances

Arbitrary Bool |
Arbitrary Char |
Arbitrary Double |
Arbitrary Float |
Arbitrary Int |
Arbitrary Int8 |
Arbitrary Int16 |
Arbitrary Int32 |
Arbitrary Int64 |
Arbitrary Integer |
Arbitrary Ordering |
Arbitrary Word |
Arbitrary Word8 |
Arbitrary Word16 |
Arbitrary Word32 |
Arbitrary Word64 |
Arbitrary () |
Arbitrary OrdC |
Arbitrary OrdB |
Arbitrary OrdA |
Arbitrary C |
Arbitrary B |
Arbitrary A |
Arbitrary a => Arbitrary [a] |
(Integral a, Arbitrary a) => Arbitrary (Ratio a) |
HasResolution a => Arbitrary (Fixed a) |
(RealFloat a, Arbitrary a) => Arbitrary (Complex a) |
Arbitrary a => Arbitrary (Maybe a) |
Arbitrary a => Arbitrary (Smart a) |
Arbitrary a => Arbitrary (Shrink2 a) |
Integral a => Arbitrary (Small a) |
(Integral a, Bounded a) => Arbitrary (Large a) |
(Num a, Ord a, Arbitrary a) => Arbitrary (NonNegative a) |
(Num a, Ord a, Arbitrary a) => Arbitrary (NonZero a) |
(Num a, Ord a, Arbitrary a) => Arbitrary (Positive a) |
Arbitrary a => Arbitrary (NonEmptyList a) |
(Ord a, Arbitrary a) => Arbitrary (OrderedList a) |
Arbitrary a => Arbitrary (Fixed a) |
Arbitrary a => Arbitrary (Blind a) |
(CoArbitrary a, Arbitrary b) => Arbitrary (a -> b) |
(Arbitrary a, Arbitrary b) => Arbitrary (Either a b) |
(Arbitrary a, Arbitrary b) => Arbitrary (a, b) |
(Arbitrary a, ShrinkState s a) => Arbitrary (Shrinking s a) |
(Function a, CoArbitrary a, Arbitrary b) => Arbitrary (Fun a b) |
(Function a, CoArbitrary a, Arbitrary b) => Arbitrary ((:->) a b) |
(Arbitrary a, Arbitrary b, Arbitrary c) => Arbitrary (a, b, c) |
(Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d) => Arbitrary (a, b, c, d) |
(Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d, Arbitrary e) => Arbitrary (a, b, c, d, e) |

class CoArbitrary a where

Used for random generation of functions.

Methods

coarbitrary :: a -> Gen b -> Gen b

Used to generate a function of type `a -> b`. The first argument is a value, the second a generator. You should use `variant` to perturb the random generator; the goal is that different values for the first argument will lead to different calls to `variant`. An example will help:

    instance CoArbitrary a => CoArbitrary [a] where
      coarbitrary []     = variant 0
      coarbitrary (x:xs) = variant 1 . coarbitrary (x,xs)

Instances

CoArbitrary Bool |
CoArbitrary Char |
CoArbitrary Double |
CoArbitrary Float |
CoArbitrary Int |
CoArbitrary Int8 |
CoArbitrary Int16 |
CoArbitrary Int32 |
CoArbitrary Int64 |
CoArbitrary Integer |
CoArbitrary Ordering |
CoArbitrary Word |
CoArbitrary Word8 |
CoArbitrary Word16 |
CoArbitrary Word32 |
CoArbitrary Word64 |
CoArbitrary () |
CoArbitrary OrdC |
CoArbitrary OrdB |
CoArbitrary OrdA |
CoArbitrary C |
CoArbitrary B |
CoArbitrary A |
CoArbitrary a => CoArbitrary [a] |
(Integral a, CoArbitrary a) => CoArbitrary (Ratio a) |
HasResolution a => CoArbitrary (Fixed a) |
(RealFloat a, CoArbitrary a) => CoArbitrary (Complex a) |
CoArbitrary a => CoArbitrary (Maybe a) |
(Arbitrary a, CoArbitrary b) => CoArbitrary (a -> b) |
(CoArbitrary a, CoArbitrary b) => CoArbitrary (Either a b) |
(CoArbitrary a, CoArbitrary b) => CoArbitrary (a, b) |
(CoArbitrary a, CoArbitrary b, CoArbitrary c) => CoArbitrary (a, b, c) |
(CoArbitrary a, CoArbitrary b, CoArbitrary c, CoArbitrary d) => CoArbitrary (a, b, c, d) |
(CoArbitrary a, CoArbitrary b, CoArbitrary c, CoArbitrary d, CoArbitrary e) => CoArbitrary (a, b, c, d, e) |

## Helper functions for implementing arbitrary

arbitrarySizedIntegral :: Integral a => Gen a

Generates an integral number. The number can be positive or negative and its maximum absolute value depends on the size parameter.

arbitrarySizedFractional :: Fractional a => Gen a

Generates a fractional number. The number can be positive or negative and its maximum absolute value depends on the size parameter.

arbitrarySizedBoundedIntegral :: (Bounded a, Integral a) => Gen a

Generates an integral number from a bounded domain. The number is chosen from the entire range of the type, but small numbers are generated more often than big numbers. Inspired by demands from Phil Wadler.

arbitraryBoundedIntegral :: (Bounded a, Integral a) => Gen a

Generates an integral number. The number is chosen uniformly from the entire range of the type. You may want to use `arbitrarySizedBoundedIntegral` instead.

arbitraryBoundedRandom :: (Bounded a, Random a) => Gen a

Generates an element of a bounded type. The element is chosen from the entire range of the type.

arbitraryBoundedEnum :: (Bounded a, Enum a) => Gen a

Generates an element of a bounded enumeration.

## Helper functions for implementing shrink

genericShrink :: (Generic a, Typeable a, RecursivelyShrink (Rep a), Subterms (Rep a)) => a -> [a]

Shrink a term to any of its immediate subterms, and also recursively shrink all subterms.

subterms :: (Generic a, Typeable a, Subterms (Rep a)) => a -> [a]

All immediate subterms of a term.

recursivelyShrink :: (Generic a, RecursivelyShrink (Rep a)) => a -> [a]

Recursively shrink all immediate subterms.

shrinkNothing :: a -> [a]

Returns no shrinking alternatives.

shrinkList :: (a -> [a]) -> [a] -> [[a]]

Shrink a list of values given a shrinking function for individual values.

shrinkIntegral :: Integral a => a -> [a]

Shrink an integral number.

shrinkRealFrac :: RealFrac a => a -> [a]

Shrink a fraction.

shrinkRealFracToInteger :: RealFrac a => a -> [a]

Shrink a fraction, but only shrink to integral values.

## Helper functions for implementing coarbitrary

variant :: Integral n => n -> Gen a -> Gen a

Modifies a generator using an integer seed.

coarbitraryIntegral :: Integral a => a -> Gen b -> Gen b

A `coarbitrary` implementation for integral numbers.

coarbitraryReal :: Real a => a -> Gen b -> Gen b

A `coarbitrary` implementation for real numbers.

coarbitraryShow :: Show a => a -> Gen b -> Gen b

`coarbitrary` helper for lazy people :-).

coarbitraryEnum :: Enum a => a -> Gen b -> Gen b

A `coarbitrary` implementation for enums.

(><) :: (Gen a -> Gen a) -> (Gen a -> Gen a) -> Gen a -> Gen a

Deprecated: Use ordinary function composition instead

Combine two generator perturbing functions, for example the results of calls to `variant` or `coarbitrary`.

## Type-level modifiers for changing generator behavior

newtype Blind a

`Blind x`: as x, but x does not have to be in the `Show` class.

Constructors

Blind |
Fields getBlind :: a

Instances

Functor Blind |
Enum a => Enum (Blind a) |
Eq a => Eq (Blind a) |
Integral a => Integral (Blind a) |
Num a => Num (Blind a) |
Ord a => Ord (Blind a) |
Real a => Real (Blind a) |
Show (Blind a) |
Arbitrary a => Arbitrary (Blind a) |

newtype Fixed a

`Fixed x`: as x, but will not be shrunk.

Constructors

Fixed |
Fields getFixed :: a

Instances

Functor Fixed |
Enum a => Enum (Fixed a) |
Eq a => Eq (Fixed a) |
Integral a => Integral (Fixed a) |
Num a => Num (Fixed a) |
Ord a => Ord (Fixed a) |
Read a => Read (Fixed a) |
Real a => Real (Fixed a) |
Show a => Show (Fixed a) |
Arbitrary a => Arbitrary (Fixed a) |

newtype OrderedList a

`Ordered xs`: guarantees that xs is ordered.

Constructors

Ordered |
Fields getOrdered :: [a]

Instances

Functor OrderedList |
Eq a => Eq (OrderedList a) |
Ord a => Ord (OrderedList a) |
Read a => Read (OrderedList a) |
Show a => Show (OrderedList a) |
(Ord a, Arbitrary a) => Arbitrary (OrderedList a) |

newtype NonEmptyList a

`NonEmpty xs`: guarantees that xs is non-empty.

Constructors

NonEmpty |
Fields getNonEmpty :: [a]

Instances

Functor NonEmptyList |
Eq a => Eq (NonEmptyList a) |
Ord a => Ord (NonEmptyList a) |
Read a => Read (NonEmptyList a) |
Show a => Show (NonEmptyList a) |
Arbitrary a => Arbitrary (NonEmptyList a) |

newtype Positive a

`Positive x`: guarantees that `x > 0`.

Constructors

Positive |
Fields getPositive :: a

Instances

Functor Positive |
Enum a => Enum (Positive a) |
Eq a => Eq (Positive a) |
Integral a => Integral (Positive a) |
Num a => Num (Positive a) |
Ord a => Ord (Positive a) |
Read a => Read (Positive a) |
Real a => Real (Positive a) |
Show a => Show (Positive a) |
(Num a, Ord a, Arbitrary a) => Arbitrary (Positive a) |

newtype NonZero a

`NonZero x`: guarantees that `x /= 0`.

Constructors

NonZero |
Fields getNonZero :: a

Instances

Functor NonZero |
Enum a => Enum (NonZero a) |
Eq a => Eq (NonZero a) |
Integral a => Integral (NonZero a) |
Num a => Num (NonZero a) |
Ord a => Ord (NonZero a) |
Read a => Read (NonZero a) |
Real a => Real (NonZero a) |
Show a => Show (NonZero a) |
(Num a, Ord a, Arbitrary a) => Arbitrary (NonZero a) |

newtype NonNegative a

`NonNegative x`: guarantees that `x >= 0`.

Constructors

NonNegative |
Fields getNonNegative :: a

Instances

Functor NonNegative |
Enum a => Enum (NonNegative a) |
Eq a => Eq (NonNegative a) |
Integral a => Integral (NonNegative a) |
Num a => Num (NonNegative a) |
Ord a => Ord (NonNegative a) |
Read a => Read (NonNegative a) |
Real a => Real (NonNegative a) |
Show a => Show (NonNegative a) |
(Num a, Ord a, Arbitrary a) => Arbitrary (NonNegative a) |

newtype Large a

`Large x`: by default, QuickCheck generates `Int`s drawn from a small range. `Large Int` gives you values drawn from the entire range instead.

Constructors

Large |
Fields getLarge :: a

Instances

Functor Large |
Enum a => Enum (Large a) |
Eq a => Eq (Large a) |
Integral a => Integral (Large a) |
Num a => Num (Large a) |
Ord a => Ord (Large a) |
Read a => Read (Large a) |
Real a => Real (Large a) |
Show a => Show (Large a) |
(Integral a, Bounded a) => Arbitrary (Large a) |

newtype Small a

`Small x`: generates values of `x` drawn from a small range. The opposite of `Large`.

Constructors

Small |
Fields getSmall :: a

Instances

Functor Small |
Enum a => Enum (Small a) |
Eq a => Eq (Small a) |
Integral a => Integral (Small a) |
Num a => Num (Small a) |
Ord a => Ord (Small a) |
Read a => Read (Small a) |
Real a => Real (Small a) |
Show a => Show (Small a) |
Integral a => Arbitrary (Small a) |

data Smart a

`Smart _ x`: tries a different order when shrinking.

Constructors

Smart Int a |

Instances

Functor Smart |
Show a => Show (Smart a) |
Arbitrary a => Arbitrary (Smart a) |

newtype Shrink2 a

`Shrink2 x`: allows 2 shrinking steps at the same time when shrinking x

Constructors

Shrink2 |
Fields getShrink2 :: a

Instances

Functor Shrink2 |
Enum a => Enum (Shrink2 a) |
Eq a => Eq (Shrink2 a) |
Integral a => Integral (Shrink2 a) |
Num a => Num (Shrink2 a) |
Ord a => Ord (Shrink2 a) |
Read a => Read (Shrink2 a) |
Real a => Real (Shrink2 a) |
Show a => Show (Shrink2 a) |
Arbitrary a => Arbitrary (Shrink2 a) |

data Shrinking s a

`Shrinking _ x`: allows for maintaining a state during shrinking.

Constructors

Shrinking s a |

Instances

Functor (Shrinking s) |
Show a => Show (Shrinking s a) |
(Arbitrary a, ShrinkState s a) => Arbitrary (Shrinking s a) |

class ShrinkState s a where

Methods

shrinkInit :: a -> s

shrinkState :: a -> s -> [(a, s)]

# Properties

data Property

The type of properties.

Instances

Testable Property |

class Testable prop where

The class of things which can be tested, i.e. turned into a property.

Minimal complete definition

property

Methods

property :: prop -> Property

Convert the thing to a property.

exhaustive :: prop -> Bool

If true, the property will only be tested once. However, if used inside a quantifier, it will be tested normally.

Instances

Testable Bool |
Testable Result |
Testable Prop |
Testable Discard |
Testable Property |
Testable prop => Testable (Gen prop) |
(Arbitrary a, Show a, Testable prop) => Testable (a -> prop) |

## Property combinators

forAll :: (Show a, Testable prop) => Gen a -> (a -> prop) -> Property

Explicit universal quantification: uses an explicitly given test case generator.

forAllShrink :: (Show a, Testable prop) => Gen a -> (a -> [a]) -> (a -> prop) -> Property

Like `forAll`, but tries to shrink the argument for failing test cases.

shrinking

Arguments

:: Testable prop |
=> (a -> [a]) | `shrink`-like function.
-> a | The original argument
-> (a -> prop) |
-> Property |

Shrinks the argument to property if it fails. Shrinking is done automatically for most types. This is only needed when you want to override the default behavior.

(==>) :: Testable prop => Bool -> prop -> Property infixr 0

Implication for properties: The resulting property holds if the first argument is `False` (in which case the test case is discarded), or if the given property holds.

(===) :: (Eq a, Show a) => a -> a -> Property infix 4

Like `==`, but prints a counterexample when it fails.

ioProperty :: Testable prop => IO prop -> Property

Do I/O inside a property. This can obviously lead to unrepeatable testcases, so use with care.

For more advanced monadic testing you may want to look at Test.QuickCheck.Monadic.

### Controlling property execution

verbose :: Testable prop => prop -> Property

Prints out the generated testcase every time the property is tested. Only variables quantified over inside the `verbose` are printed.

once :: Testable prop => prop -> Property

Modifies a property so that it only will be tested once.

within :: Testable prop => Int -> prop -> Property

Considers a property failed if it does not complete within the given number of microseconds.

noShrinking :: Testable prop => prop -> Property

Disables shrinking for a property altogether.

### Conjunction and disjunction

(.&.) :: (Testable prop1, Testable prop2) => prop1 -> prop2 -> Property infixr 1

Nondeterministic choice: `p1` `.&.` `p2` picks randomly one of `p1` and `p2` to test. If you test the property 100 times it makes 100 random choices.

(.&&.) :: (Testable prop1, Testable prop2) => prop1 -> prop2 -> Property infixr 1

Conjunction: `p1` `.&&.` `p2` passes if both `p1` and `p2` pass.

conjoin :: Testable prop => [prop] -> Property

Take the conjunction of several properties.

(.||.) :: (Testable prop1, Testable prop2) => prop1 -> prop2 -> Property infixr 1

Disjunction: `p1` `.||.` `p2` passes unless `p1` and `p2` simultaneously fail.

disjoin :: Testable prop => [prop] -> Property

Take the disjunction of several properties.

### What to do on failure

counterexample :: Testable prop => String -> prop -> Property

Adds the given string to the counterexample.

printTestCase :: Testable prop => String -> prop -> Property

Deprecated: Use counterexample instead

Adds the given string to the counterexample.

whenFail :: Testable prop => IO () -> prop -> Property

Performs an `IO` action after the last failure of a property.

whenFail' :: Testable prop => IO () -> prop -> Property

Performs an `IO` action every time a property fails. Thus, if shrinking is done, this can be used to keep track of the failures along the way.

expectFailure :: Testable prop => prop -> Property

Indicates that a property is supposed to fail. QuickCheck will report an error if it does not fail.

### Analysing test distribution

label :: Testable prop => String -> prop -> Property

Attaches a label to a property. This is used for reporting test case distribution.

collect :: (Show a, Testable prop) => a -> prop -> Property

Labels a property with a value:

    collect x = label (show x)

classify

Arguments

:: Testable prop |
=> Bool | `True` if the test case should be labelled.
-> String | Label.
-> prop |
-> Property |

Conditionally labels test case.

cover

Arguments

:: Testable prop |
=> Bool | `True` if the test case belongs to the class.
-> Int | The required percentage (0-100) of test cases.
-> String | Label for the test case class.
-> prop |
-> Property |

Checks that at least the given proportion of the test cases belong to the given class.

### Miscellaneous

data Discard

If a property returns `Discard`, the current test case is discarded, the same as if a precondition was false.

Constructors

Discard |

Instances

Testable Discard |

discard :: a

A special exception that makes QuickCheck discard the test case. Normally you should use `==>`, but if for some reason this isn't possible (e.g. you are deep inside a generator), use `discard` instead.

mapSize :: Testable prop => (Int -> Int) -> prop -> Property

Changes the maximum test case size for a property.