Safe Haskell  Safe 

Language  Haskell2010 
 Running tests
 The
Arbitrary
typeclass: generation of random values  The
Gen
monad: combinators for building random generators  The
Function
typeclass: generation of random shrinkable, showable functions  The
CoArbitrary
typeclass: generation of functions the oldfashioned way  Typelevel modifiers for changing generator behavior
 Property combinators
 Analysing test case distribution
The QuickCheck manual gives detailed information about using QuickCheck effectively. You can also try https://begriffs.com/posts/20170114designusequickcheck.html, a tutorial written by a user of QuickCheck.
To start using QuickCheck, write down your property as a function returning Bool
.
For example, to check that reversing a list twice gives back the same list you can write:
import Test.QuickCheck prop_reverse :: [Int] > Bool prop_reverse xs = reverse (reverse xs) == xs
You can then use QuickCheck to test prop_reverse
on 100 random lists:
>>>
quickCheck prop_reverse
+++ OK, passed 100 tests.
To run more tests you can use the withMaxSuccess
combinator:
>>>
quickCheck (withMaxSuccess 10000 prop_reverse)
+++ OK, passed 10000 tests.
To use QuickCheck on your own data types you will need to write Arbitrary
instances for those types. See the
QuickCheck manual for
details about how to do that.
Synopsis
 quickCheck :: Testable prop => prop > IO ()
 data Args = Args {
 replay :: Maybe (QCGen, Int)
 maxSuccess :: Int
 maxDiscardRatio :: Int
 maxSize :: Int
 chatty :: Bool
 maxShrinks :: Int
 data Result
 = Success { }
  GaveUp { }
  Failure {
 numTests :: Int
 numDiscarded :: Int
 numShrinks :: Int
 numShrinkTries :: Int
 numShrinkFinal :: Int
 usedSeed :: QCGen
 usedSize :: Int
 reason :: String
 theException :: Maybe AnException
 output :: String
 failingTestCase :: [String]
 failingLabels :: [String]
 failingClasses :: Set String
  NoExpectedFailure { }
 stdArgs :: Args
 quickCheckWith :: Testable prop => Args > prop > IO ()
 quickCheckWithResult :: Testable prop => Args > prop > IO Result
 quickCheckResult :: Testable prop => prop > IO Result
 isSuccess :: Result > Bool
 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
 allProperties :: Q Exp
 polyQuickCheck :: Name > ExpQ
 polyVerboseCheck :: Name > ExpQ
 monomorphic :: Name > ExpQ
 class Arbitrary a where
 genericShrink :: (Generic a, RecursivelyShrink (Rep a), GSubterms (Rep a) a) => a > [a]
 subterms :: (Generic a, GSubterms (Rep a) a) => a > [a]
 recursivelyShrink :: (Generic a, RecursivelyShrink (Rep a)) => a > [a]
 shrinkNothing :: a > [a]
 shrinkList :: (a > [a]) > [a] > [[a]]
 shrinkMap :: Arbitrary a => (a > b) > (b > a) > b > [b]
 shrinkMapBy :: (a > b) > (b > a) > (a > [a]) > b > [b]
 shrinkIntegral :: Integral a => a > [a]
 shrinkRealFrac :: RealFrac a => a > [a]
 shrinkDecimal :: RealFrac a => a > [a]
 class Arbitrary1 f where
 liftArbitrary :: Gen a > Gen (f a)
 liftShrink :: (a > [a]) > f a > [f a]
 arbitrary1 :: (Arbitrary1 f, Arbitrary a) => Gen (f a)
 shrink1 :: (Arbitrary1 f, Arbitrary a) => f a > [f a]
 class Arbitrary2 f where
 liftArbitrary2 :: Gen a > Gen b > Gen (f a b)
 liftShrink2 :: (a > [a]) > (b > [b]) > f a b > [f a b]
 arbitrary2 :: (Arbitrary2 f, Arbitrary a, Arbitrary b) => Gen (f a b)
 shrink2 :: (Arbitrary2 f, Arbitrary a, Arbitrary b) => f a b > [f a b]
 data Gen a
 choose :: Random a => (a, a) > Gen a
 chooseInt :: (Int, Int) > Gen Int
 chooseInteger :: (Integer, Integer) > Gen Integer
 chooseBoundedIntegral :: (Bounded a, Integral a) => (a, a) > Gen a
 chooseEnum :: Enum a => (a, a) > Gen a
 chooseAny :: Random 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
 getSize :: Gen Int
 resize :: Int > Gen a > Gen a
 scale :: (Int > Int) > Gen a > Gen a
 suchThat :: Gen a > (a > Bool) > Gen a
 suchThatMap :: Gen a > (a > Maybe b) > Gen b
 suchThatMaybe :: Gen a > (a > Bool) > Gen (Maybe a)
 applyArbitrary2 :: (Arbitrary a, Arbitrary b) => (a > b > r) > Gen r
 applyArbitrary3 :: (Arbitrary a, Arbitrary b, Arbitrary c) => (a > b > c > r) > Gen r
 applyArbitrary4 :: (Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d) => (a > b > c > d > r) > Gen r
 listOf :: Gen a > Gen [a]
 listOf1 :: Gen a > Gen [a]
 vectorOf :: Int > Gen a > Gen [a]
 vector :: Arbitrary a => Int > Gen [a]
 infiniteListOf :: Gen a > Gen [a]
 infiniteList :: Arbitrary a => Gen [a]
 shuffle :: [a] > Gen [a]
 sublistOf :: [a] > Gen [a]
 orderedList :: (Ord a, Arbitrary a) => Gen [a]
 arbitrarySizedIntegral :: Integral a => Gen a
 arbitrarySizedNatural :: 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
 arbitraryUnicodeChar :: Gen Char
 arbitraryASCIIChar :: Gen Char
 arbitraryPrintableChar :: Gen Char
 generate :: Gen a > IO a
 sample :: Show a => Gen a > IO ()
 sample' :: Gen a > IO [a]
 data Fun a b = Fun (a :> b, b, Shrunk) (a > b)
 applyFun :: Fun a b > a > b
 applyFun2 :: Fun (a, b) c > a > b > c
 applyFun3 :: Fun (a, b, c) d > a > b > c > d
 pattern Fn :: (a > b) > Fun a b
 pattern Fn2 :: (a > b > c) > Fun (a, b) c
 pattern Fn3 :: (a > b > c > d) > Fun (a, b, c) d
 class Function a where
 functionMap :: Function b => (a > b) > (b > a) > (a > c) > a :> c
 functionShow :: (Show a, Read a) => (a > c) > a :> c
 functionIntegral :: Integral a => (a > b) > a :> b
 functionRealFrac :: RealFrac a => (a > b) > a :> b
 functionBoundedEnum :: (Eq a, Bounded a, Enum a) => (a > b) > a :> b
 functionVoid :: (forall b. void > b) > void :> c
 class CoArbitrary a where
 coarbitrary :: a > Gen b > Gen b
 genericCoarbitrary :: (Generic a, GCoArbitrary (Rep a)) => a > Gen b > Gen b
 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]
 data InfiniteList a = InfiniteList {
 getInfiniteList :: [a]
 infiniteListInternalData :: InfiniteListInternalData a
 newtype SortedList a = Sorted {
 getSorted :: [a]
 newtype Positive a = Positive {
 getPositive :: a
 newtype Negative a = Negative {
 getNegative :: a
 newtype NonZero a = NonZero {
 getNonZero :: a
 newtype NonNegative a = NonNegative {
 getNonNegative :: a
 newtype NonPositive a = NonPositive {
 getNonPositive :: 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)]
 newtype ASCIIString = ASCIIString {}
 newtype UnicodeString = UnicodeString {}
 newtype PrintableString = PrintableString {}
 data Property
 class Testable prop where
 forAll :: (Show a, Testable prop) => Gen a > (a > prop) > Property
 forAllShrink :: (Show a, Testable prop) => Gen a > (a > [a]) > (a > prop) > Property
 forAllShow :: Testable prop => Gen a > (a > String) > (a > prop) > Property
 forAllShrinkShow :: Testable prop => Gen a > (a > [a]) > (a > String) > (a > prop) > Property
 forAllBlind :: Testable prop => Gen a > (a > prop) > Property
 forAllShrinkBlind :: Testable prop => Gen a > (a > [a]) > (a > prop) > Property
 shrinking :: Testable prop => (a > [a]) > a > (a > prop) > Property
 (==>) :: Testable prop => Bool > prop > Property
 data Discard = Discard
 discard :: a
 (===) :: (Eq a, Show a) => a > a > Property
 (=/=) :: (Eq a, Show a) => a > a > Property
 total :: NFData a => a > Property
 ioProperty :: Testable prop => IO prop > Property
 idempotentIOProperty :: Testable prop => IO prop > Property
 verbose :: Testable prop => prop > Property
 verboseShrinking :: Testable prop => prop > Property
 noShrinking :: Testable prop => prop > Property
 withMaxSuccess :: Testable prop => Int > prop > Property
 within :: Testable prop => Int > prop > Property
 once :: Testable prop => prop > Property
 again :: Testable prop => prop > Property
 mapSize :: Testable prop => (Int > Int) > 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
 tabulate :: Testable prop => String > [String] > prop > Property
 cover :: Testable prop => Double > Bool > String > prop > Property
 coverTable :: Testable prop => String > [(String, Double)] > prop > Property
 checkCoverage :: Testable prop => prop > Property
 checkCoverageWith :: Testable prop => Confidence > prop > Property
 data Confidence = Confidence {}
 stdConfidence :: Confidence
 labelledExamples :: Testable prop => prop > IO ()
 labelledExamplesWith :: Testable prop => Args > prop > IO ()
 labelledExamplesWithResult :: Testable prop => Args > prop > IO Result
 labelledExamplesResult :: Testable prop => prop > IO Result
Running tests
quickCheck :: Testable prop => prop > IO () Source #
Tests a property and prints the results to stdout
.
By default up to 100 tests are performed, which may not be enough
to find all bugs. To run more tests, use withMaxSuccess
.
If you want to get the counterexample as a Haskell value, rather than just printing it, try the quickcheckwithcounterexamples package.
Args specifies arguments to the QuickCheck driver
Args  

Result represents the test result
Success  A successful test run 
 
GaveUp  Given up 
 
Failure  A failed test run 
 
NoExpectedFailure  A property that should have failed did not 

quickCheckWith :: Testable prop => Args > prop > IO () Source #
Tests a property, using test arguments, and prints the results to stdout
.
quickCheckWithResult :: Testable prop => Args > prop > IO Result Source #
Tests a property, using test arguments, produces a test result, and prints the results to stdout
.
quickCheckResult :: Testable prop => prop > IO Result Source #
Tests a property, produces a test result, and prints the results to stdout
.
Running tests verbosely
verboseCheck :: Testable prop => prop > IO () Source #
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
Note: for technical reasons, the test case is printed out after
the property is tested. To debug a property that goes into an
infinite loop, use within
to add a timeout instead.
verboseCheckWith :: Testable prop => Args > prop > IO () Source #
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
.
Note: for technical reasons, the test case is printed out after
the property is tested. To debug a property that goes into an
infinite loop, use within
to add a timeout instead.
verboseCheckWithResult :: Testable prop => Args > prop > IO Result Source #
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
.
Note: for technical reasons, the test case is printed out after
the property is tested. To debug a property that goes into an
infinite loop, use within
to add a timeout instead.
verboseCheckResult :: Testable prop => prop > IO Result Source #
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
.
Note: for technical reasons, the test case is printed out after
the property is tested. To debug a property that goes into an
infinite loop, use within
to add a timeout instead.
Testing all properties in a module
These functions test all properties in the current module, using
Template Haskell. You need to have a {# LANGUAGE TemplateHaskell #}
pragma in your module for any of these to work.
quickCheckAll :: Q Exp Source #
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.
To use quickCheckAll
, add a definition to your module along
the lines of
return [] runTests = $quickCheckAll
and then execute runTests
.
Note: the bizarre return []
in the example above is needed on
GHC 7.8 and later; without it, quickCheckAll
will not be able to find
any of the properties. For the curious, the return []
is a
Template Haskell splice that makes GHC insert the empty list
of declarations at that point in the program; GHC typechecks
everything before the return []
before it starts on the rest
of the module, which means that the later call to quickCheckAll
can see everything that was defined before the return []
. Yikes!
verboseCheckAll :: Q Exp Source #
Test all properties in the current module.
This is just a convenience function that combines quickCheckAll
and verbose
.
verboseCheckAll
has the same issue with scoping as quickCheckAll
:
see the note there about return []
.
forAllProperties :: Q Exp Source #
Test all properties in the current module, using a custom
quickCheck
function. The same caveats as with quickCheckAll
apply.
$
has type forAllProperties
(
.
An example invocation is Property
> IO
Result
) > IO
Bool
$
,
which does the same thing as forAllProperties
quickCheckResult
$
.quickCheckAll
forAllProperties
has the same issue with scoping as quickCheckAll
:
see the note there about return []
.
allProperties :: Q Exp Source #
List all properties in the current module.
$
has type allProperties
[(
.String
, Property
)]
allProperties
has the same issue with scoping as quickCheckAll
:
see the note there about return []
.
Testing polymorphic properties
polyQuickCheck :: Name > ExpQ Source #
Test a polymorphic property, defaulting all type variables to Integer
.
Invoke as $(
, where polyQuickCheck
'prop)prop
is a property.
Note that just evaluating
in GHCi will seem to
work, but will silently default all type variables to quickCheck
prop()
!
$(
means the same as
polyQuickCheck
'prop)
.
If you want to supply custom arguments to quickCheck
$(monomorphic
'prop)polyQuickCheck
,
you will have to combine quickCheckWith
and monomorphic
yourself.
If you want to use polyQuickCheck
in the same file where you defined the
property, the same scoping problems pop up as in quickCheckAll
:
see the note there about return []
.
polyVerboseCheck :: Name > ExpQ Source #
Test a polymorphic property, defaulting all type variables to Integer
.
This is just a convenience function that combines verboseCheck
and monomorphic
.
If you want to use polyVerboseCheck
in the same file where you defined the
property, the same scoping problems pop up as in quickCheckAll
:
see the note there about return []
.
monomorphic :: Name > ExpQ Source #
Monomorphise an arbitrary property by defaulting all type variables to Integer
.
For example, if f
has type
then Ord
a => [a] > [a]$(
has type monomorphic
'f)[
.Integer
] > [Integer
]
If you want to use monomorphic
in the same file where you defined the
property, the same scoping problems pop up as in quickCheckAll
:
see the note there about return []
.
The Arbitrary
typeclass: generation of random values
class Arbitrary a where Source #
Random generation and shrinking of values.
QuickCheck provides Arbitrary
instances for most types in base
,
except those which incur extra dependencies.
For a wider range of Arbitrary
instances see the
quickcheckinstances
package.
A generator for values of the given type.
It is worth spending time thinking about what sort of test data
you want  good generators are often the difference between
finding bugs and not finding them. You can use sample
,
label
and classify
to check the quality of your test data.
There is no generic arbitrary
implementation included because we don't
know how to make a highquality one. If you want one, consider using the
testingfeat or
genericrandom packages.
The QuickCheck manual goes into detail on how to write good generators. Make sure to look at it, especially if your type is recursive!
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. If your data type has no special invariants, you can
enable shrinking by defining shrink =
, but by customising
the behaviour of genericShrink
shrink
you can often get simpler counterexamples.
Most implementations of shrink
should try at least three things:
 Shrink a term to any of its immediate subterms.
You can use
subterms
to do this.  Recursively apply
shrink
to all immediate subterms. You can userecursivelyShrink
to do this.  Typespecific 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 shrinkx
,l
andr
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.
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
as this shrinks shrink
x = Nil:genericShrink
xNil
to Nil
, and shrinking will go into an
infinite loop.
If all this leaves you bewildered, you might try
to begin with,
after deriving shrink
= genericShrink
Generic
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
Helper functions for implementing shrink
genericShrink :: (Generic a, RecursivelyShrink (Rep a), GSubterms (Rep a) a) => a > [a] Source #
Shrink a term to any of its immediate subterms, and also recursively shrink all subterms.
recursivelyShrink :: (Generic a, RecursivelyShrink (Rep a)) => a > [a] Source #
Recursively shrink all immediate subterms.
shrinkNothing :: a > [a] Source #
Returns no shrinking alternatives.
shrinkList :: (a > [a]) > [a] > [[a]] Source #
Shrink a list of values given a shrinking function for individual values.
shrinkMap :: Arbitrary a => (a > b) > (b > a) > b > [b] Source #
Map a shrink function to another domain. This is handy if your data type has special invariants, but is almost isomorphic to some other type.
shrinkOrderedList :: (Ord a, Arbitrary a) => [a] > [[a]] shrinkOrderedList = shrinkMap sort id shrinkSet :: (Ord a, Arbitrary a) => Set a > Set [a] shrinkSet = shrinkMap fromList toList
shrinkMapBy :: (a > b) > (b > a) > (a > [a]) > b > [b] Source #
Nonoverloaded version of shrinkMap
.
shrinkIntegral :: Integral a => a > [a] Source #
Shrink an integral number.
shrinkRealFrac :: RealFrac a => a > [a] Source #
Shrink a fraction, preferring numbers with smaller
numerators or denominators. See also shrinkDecimal
.
shrinkDecimal :: RealFrac a => a > [a] Source #
Shrink a real number, preferring numbers with shorter
decimal representations. See also shrinkRealFrac
.
Lifting of Arbitrary
to unary and binary type constructors
class Arbitrary1 f where Source #
Lifting of the Arbitrary
class to unary type constructors.
liftArbitrary :: Gen a > Gen (f a) Source #
liftShrink :: (a > [a]) > f a > [f a] Source #
Instances
arbitrary1 :: (Arbitrary1 f, Arbitrary a) => Gen (f a) Source #
shrink1 :: (Arbitrary1 f, Arbitrary a) => f a > [f a] Source #
class Arbitrary2 f where Source #
Lifting of the Arbitrary
class to binary type constructors.
liftArbitrary2 :: Gen a > Gen b > Gen (f a b) Source #
liftShrink2 :: (a > [a]) > (b > [b]) > f a b > [f a b] Source #
Instances
Arbitrary2 Either Source #  
Defined in Test.QuickCheck.Arbitrary  
Arbitrary2 (,) Source #  
Defined in Test.QuickCheck.Arbitrary liftArbitrary2 :: Gen a > Gen b > Gen (a, b) Source # liftShrink2 :: (a > [a]) > (b > [b]) > (a, b) > [(a, b)] Source #  
Arbitrary2 (Const :: Type > Type > Type) Source #  
Defined in Test.QuickCheck.Arbitrary  
Arbitrary2 (Constant :: Type > Type > Type) Source #  
Defined in Test.QuickCheck.Arbitrary 
arbitrary2 :: (Arbitrary2 f, Arbitrary a, Arbitrary b) => Gen (f a b) Source #
The Gen
monad: combinators for building random generators
A generator for values of type a
.
The thirdparty packages
QuickCheckGenT
and
quickchecktransformer
provide monad transformer versions of Gen
.
Generator combinators
choose :: Random a => (a, a) > Gen a Source #
Generates a random element in the given inclusive range.
For integral and enumerated types, the specialised variants of
choose
below run much quicker.
chooseBoundedIntegral :: (Bounded a, Integral a) => (a, a) > Gen a Source #
A fast implementation of choose
for bounded integral types.
chooseEnum :: Enum a => (a, a) > Gen a Source #
A fast implementation of choose
for enumerated types.
oneof :: [Gen a] > Gen a Source #
Randomly uses one of the given generators. The input list must be nonempty.
frequency :: [(Int, Gen a)] > Gen a Source #
Chooses one of the given generators, with a weighted random distribution. The input list must be nonempty.
elements :: [a] > Gen a Source #
Generates one of the given values. The input list must be nonempty.
growingElements :: [a] > Gen a Source #
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 nonempty.
sized :: (Int > Gen a) > Gen a Source #
Used to construct generators that depend on the size parameter.
For example, listOf
, which uses the size parameter as an upper bound on
length of lists it generates, can be defined like this:
listOf :: Gen a > Gen [a] listOf gen = sized $ \n > do k < choose (0,n) vectorOf k gen
You can also do this using getSize
.
Returns the size parameter. Used to construct generators that depend on the size parameter.
For example, listOf
, which uses the size parameter as an upper bound on
length of lists it generates, can be defined like this:
listOf :: Gen a > Gen [a] listOf gen = do n < getSize k < choose (0,n) vectorOf k gen
You can also do this using sized
.
resize :: Int > Gen a > Gen a Source #
Overrides the size parameter. Returns a generator which uses the given size instead of the runtimesize parameter.
scale :: (Int > Int) > Gen a > Gen a Source #
Adjust the size parameter, by transforming it with the given function.
suchThatMap :: Gen a > (a > Maybe b) > Gen b Source #
Generates a value for which the given function returns a Just
, and then
applies the function.
suchThatMaybe :: Gen a > (a > Bool) > Gen (Maybe a) Source #
Tries to generate a value that satisfies a predicate.
If it fails to do so after enough attempts, returns Nothing
.
applyArbitrary2 :: (Arbitrary a, Arbitrary b) => (a > b > r) > Gen r Source #
Apply a binary function to random arguments.
applyArbitrary3 :: (Arbitrary a, Arbitrary b, Arbitrary c) => (a > b > c > r) > Gen r Source #
Apply a ternary function to random arguments.
applyArbitrary4 :: (Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d) => (a > b > c > d > r) > Gen r Source #
Apply a function of arity 4 to random arguments.
Generators for lists
listOf :: Gen a > Gen [a] Source #
Generates a list of random length. The maximum length depends on the size parameter.
listOf1 :: Gen a > Gen [a] Source #
Generates a nonempty list of random length. The maximum length depends on the size parameter.
infiniteListOf :: Gen a > Gen [a] Source #
Generates an infinite list.
infiniteList :: Arbitrary a => Gen [a] Source #
Generates an infinite list.
Generators for particular types
arbitrarySizedIntegral :: Integral a => Gen a Source #
Generates an integral number. The number can be positive or negative and its maximum absolute value depends on the size parameter.
arbitrarySizedNatural :: Integral a => Gen a Source #
Generates a natural number. The number's maximum value depends on the size parameter.
arbitrarySizedFractional :: Fractional a => Gen a Source #
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 Source #
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 Source #
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 Source #
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 Source #
Generates an element of a bounded enumeration.
arbitraryUnicodeChar :: Gen Char Source #
Generates any Unicode character (but not a surrogate)
arbitraryASCIIChar :: Gen Char Source #
Generates a random ASCII character (0127).
arbitraryPrintableChar :: Gen Char Source #
Generates a printable Unicode character.
Running generators
generate :: Gen a > IO a Source #
Run a generator. The size passed to the generator is always 30;
if you want another size then you should explicitly use resize
.
Debugging generators
The Function
typeclass: generation of random shrinkable, showable functions
Example of use:
>>>
:{
>>>
let prop :: Fun String Integer > Bool
>>>
prop (Fun _ f) = f "monkey" == f "banana"  f "banana" == f "elephant"
>>>
:}
>>>
quickCheck prop
*** Failed! Falsified (after 3 tests and 134 shrinks): {"elephant">1, "monkey">1, _>0}
To generate random values of type
,
you must have an instance Fun
a b
.
If your type has a Function
aShow
instance, you can use functionShow
to write the instance; otherwise,
use functionMap
to give a bijection between your type and a type that is already an instance of Function
.
See the
instance for an example of the latter.Function
[a]
For more information, see the paper "Shrinking and showing functions" by Koen Claessen.
Generation of random shrinkable, showable functions.
To generate random values of type
,
you must have an instance Fun
a b
.Function
a
applyFun :: Fun a b > a > b Source #
Extracts the value of a function.
Fn
is the pattern equivalent of this function.
prop :: Fun String Integer > Bool prop f = applyFun f "banana" == applyFun f "monkey"  applyFun f "banana" == applyFun f "elephant"
applyFun2 :: Fun (a, b) c > a > b > c Source #
Extracts the value of a binary function.
Fn2
is the pattern equivalent of this function.
prop_zipWith :: Fun (Int, Bool) Char > [Int] > [Bool] > Bool prop_zipWith f xs ys = zipWith (applyFun2 f) xs ys == [ applyFun2 f x y  (x, y) < zip xs ys]
applyFun3 :: Fun (a, b, c) d > a > b > c > d Source #
Extracts the value of a ternary function. Fn3
is the
pattern equivalent of this function.
pattern Fn :: (a > b) > Fun a b Source #
A modifier for testing functions.
prop :: Fun String Integer > Bool prop (Fn f) = f "banana" == f "monkey"  f "banana" == f "elephant"
pattern Fn2 :: (a > b > c) > Fun (a, b) c Source #
A modifier for testing binary functions.
prop_zipWith :: Fun (Int, Bool) Char > [Int] > [Bool] > Bool prop_zipWith (Fn2 f) xs ys = zipWith f xs ys == [ f x y  (x, y) < zip xs ys]
pattern Fn3 :: (a > b > c > d) > Fun (a, b, c) d Source #
A modifier for testing ternary functions.
class Function a where Source #
The class Function a
is used for random generation of showable
functions of type a > b
.
There is a default implementation for function
, which you can use
if your type has structural equality. Otherwise, you can normally
use functionMap
or functionShow
.
Nothing
Instances
functionMap :: Function b => (a > b) > (b > a) > (a > c) > a :> c Source #
functionIntegral :: Integral a => (a > b) > a :> b Source #
functionRealFrac :: RealFrac a => (a > b) > a :> b Source #
functionVoid :: (forall b. void > b) > void :> c Source #
The CoArbitrary
typeclass: generation of functions the oldfashioned way
class CoArbitrary a where Source #
Used for random generation of functions.
You should consider using Fun
instead, which
can show the generated functions as strings.
If you are using a recent GHC, there is a default definition of
coarbitrary
using genericCoarbitrary
, so if your type has a
Generic
instance it's enough to say
instance CoArbitrary MyType
You should only use genericCoarbitrary
for data types where
equality is structural, i.e. if you can't have two different
representations of the same value. An example where it's not
safe is sets implemented using binary search trees: the same
set can be represented as several different trees.
Here you would have to explicitly define
coarbitrary s = coarbitrary (toList s)
.
Nothing
coarbitrary :: a > Gen b > Gen b Source #
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
genericCoarbitrary :: (Generic a, GCoArbitrary (Rep a)) => a > Gen b > Gen b Source #
Generic CoArbitrary implementation.
coarbitraryIntegral :: Integral a => a > Gen b > Gen b Source #
A coarbitrary
implementation for integral numbers.
coarbitraryReal :: Real a => a > Gen b > Gen b Source #
A coarbitrary
implementation for real numbers.
coarbitraryShow :: Show a => a > Gen b > Gen b Source #
coarbitrary
helper for lazy people :).
coarbitraryEnum :: Enum a => a > Gen b > Gen b Source #
A coarbitrary
implementation for enums.
(><) :: (Gen a > Gen a) > (Gen a > Gen a) > Gen a > Gen a Source #
Deprecated: Use ordinary function composition instead
Combine two generator perturbing functions, for example the
results of calls to variant
or coarbitrary
.
Typelevel modifiers for changing generator behavior
These types do things such as restricting the kind of test data that can be generated. They can be patternmatched on in properties as a stylistic alternative to using explicit quantification.
Examples:
 Functions cannot be shown (but seeFunction
) prop_TakeDropWhile (Blind
p) (xs :: [A
]) = takeWhile p xs ++ dropWhile p xs == xs
prop_TakeDrop (NonNegative
n) (xs :: [A
]) = take n xs ++ drop n xs == xs
 cycle does not work for empty lists prop_Cycle (NonNegative
n) (NonEmpty
(xs :: [A
])) = take n (cycle xs) == take n (xs ++ cycle xs)
 Instead offorAll
orderedList
prop_Sort (Ordered
(xs :: [OrdA
])) = sort xs == xs
Blind x
: as x, but x does not have to be in the Show
class.
Instances
Functor Blind Source #  
Enum a => Enum (Blind a) Source #  
Eq a => Eq (Blind a) Source #  
Integral a => Integral (Blind a) Source #  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Blind a) Source #  
Ord a => Ord (Blind a) Source #  
Real a => Real (Blind a) Source #  
Defined in Test.QuickCheck.Modifiers toRational :: Blind a > Rational #  
Show (Blind a) Source #  
Arbitrary a => Arbitrary (Blind a) Source #  
Fixed x
: as x, but will not be shrunk.
Instances
Functor Fixed Source #  
Enum a => Enum (Fixed a) Source #  
Eq a => Eq (Fixed a) Source #  
Integral a => Integral (Fixed a) Source #  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Fixed a) Source #  
Ord a => Ord (Fixed a) Source #  
Read a => Read (Fixed a) Source #  
Real a => Real (Fixed a) Source #  
Defined in Test.QuickCheck.Modifiers toRational :: Fixed a > Rational #  
Show a => Show (Fixed a) Source #  
Arbitrary a => Arbitrary (Fixed a) Source #  
newtype OrderedList a Source #
Ordered xs
: guarantees that xs is ordered.
Ordered  

Instances
newtype NonEmptyList a Source #
NonEmpty xs
: guarantees that xs is nonempty.
NonEmpty  

Instances
data InfiniteList a Source #
InfiniteList xs _
: guarantees that xs is an infinite list.
When a counterexample is found, only prints the prefix of xs
that was used by the program.
Here is a contrived example property:
prop_take_10 :: InfiniteList Char > Bool prop_take_10 (InfiniteList xs _) = or [ x == 'a'  x < take 10 xs ]
In the following counterexample, the list must start with "bbbbbbbbbb"
but
the remaining (infinite) part can contain anything:
>>>
quickCheck prop_take_10
*** Failed! Falsified (after 1 test and 14 shrinks): "bbbbbbbbbb" ++ ...
InfiniteList  

Instances
Show a => Show (InfiniteList a) Source #  
Defined in Test.QuickCheck.Modifiers showsPrec :: Int > InfiniteList a > ShowS # show :: InfiniteList a > String # showList :: [InfiniteList a] > ShowS #  
Arbitrary a => Arbitrary (InfiniteList a) Source #  
Defined in Test.QuickCheck.Modifiers arbitrary :: Gen (InfiniteList a) Source # shrink :: InfiniteList a > [InfiniteList a] Source # 
newtype SortedList a Source #
Sorted xs
: guarantees that xs is sorted.
Instances
Positive x
: guarantees that x > 0
.
Positive  

Instances
Functor Positive Source #  
Enum a => Enum (Positive a) Source #  
Defined in Test.QuickCheck.Modifiers succ :: Positive a > Positive a # pred :: Positive a > Positive a # fromEnum :: Positive a > Int # enumFrom :: Positive a > [Positive a] # enumFromThen :: Positive a > Positive a > [Positive a] # enumFromTo :: Positive a > Positive a > [Positive a] # enumFromThenTo :: Positive a > Positive a > Positive a > [Positive a] #  
Eq a => Eq (Positive a) Source #  
Ord a => Ord (Positive a) Source #  
Read a => Read (Positive a) Source #  
Show a => Show (Positive a) Source #  
(Num a, Ord a, Arbitrary a) => Arbitrary (Positive a) Source #  
Negative x
: guarantees that x < 0
.
Negative  

Instances
Functor Negative Source #  
Enum a => Enum (Negative a) Source #  
Defined in Test.QuickCheck.Modifiers succ :: Negative a > Negative a # pred :: Negative a > Negative a # fromEnum :: Negative a > Int # enumFrom :: Negative a > [Negative a] # enumFromThen :: Negative a > Negative a > [Negative a] # enumFromTo :: Negative a > Negative a > [Negative a] # enumFromThenTo :: Negative a > Negative a > Negative a > [Negative a] #  
Eq a => Eq (Negative a) Source #  
Ord a => Ord (Negative a) Source #  
Read a => Read (Negative a) Source #  
Show a => Show (Negative a) Source #  
(Num a, Ord a, Arbitrary a) => Arbitrary (Negative a) Source #  
NonZero x
: guarantees that x /= 0
.
NonZero  

Instances
Functor NonZero Source #  
Enum a => Enum (NonZero a) Source #  
Defined in Test.QuickCheck.Modifiers succ :: NonZero a > NonZero a # pred :: NonZero a > NonZero a # fromEnum :: NonZero a > Int # enumFrom :: NonZero a > [NonZero a] # enumFromThen :: NonZero a > NonZero a > [NonZero a] # enumFromTo :: NonZero a > NonZero a > [NonZero a] # enumFromThenTo :: NonZero a > NonZero a > NonZero a > [NonZero a] #  
Eq a => Eq (NonZero a) Source #  
Ord a => Ord (NonZero a) Source #  
Defined in Test.QuickCheck.Modifiers  
Read a => Read (NonZero a) Source #  
Show a => Show (NonZero a) Source #  
(Num a, Eq a, Arbitrary a) => Arbitrary (NonZero a) Source #  
newtype NonNegative a Source #
NonNegative x
: guarantees that x >= 0
.
Instances
newtype NonPositive a Source #
NonPositive x
: guarantees that x <= 0
.
Instances
Large x
: by default, QuickCheck generates Int
s drawn from a small
range. Large Int
gives you values drawn from the entire range instead.
Instances
Functor Large Source #  
Enum a => Enum (Large a) Source #  
Eq a => Eq (Large a) Source #  
Integral a => Integral (Large a) Source #  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Large a) Source #  
Ord a => Ord (Large a) Source #  
Read a => Read (Large a) Source #  
Real a => Real (Large a) Source #  
Defined in Test.QuickCheck.Modifiers toRational :: Large a > Rational #  
Show a => Show (Large a) Source #  
Ix a => Ix (Large a) Source #  
Defined in Test.QuickCheck.Modifiers  
(Integral a, Bounded a) => Arbitrary (Large a) Source #  
Small x
: generates values of x
drawn from a small range.
The opposite of Large
.
Instances
Functor Small Source #  
Enum a => Enum (Small a) Source #  
Eq a => Eq (Small a) Source #  
Integral a => Integral (Small a) Source #  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Small a) Source #  
Ord a => Ord (Small a) Source #  
Read a => Read (Small a) Source #  
Real a => Real (Small a) Source #  
Defined in Test.QuickCheck.Modifiers toRational :: Small a > Rational #  
Show a => Show (Small a) Source #  
Ix a => Ix (Small a) Source #  
Defined in Test.QuickCheck.Modifiers  
Integral a => Arbitrary (Small a) Source #  
Smart _ x
: tries a different order when shrinking.
Shrink2 x
: allows 2 shrinking steps at the same time when shrinking x
Shrink2  

Instances
Functor Shrink2 Source #  
Enum a => Enum (Shrink2 a) Source #  
Defined in Test.QuickCheck.Modifiers succ :: Shrink2 a > Shrink2 a # pred :: Shrink2 a > Shrink2 a # fromEnum :: Shrink2 a > Int # enumFrom :: Shrink2 a > [Shrink2 a] # enumFromThen :: Shrink2 a > Shrink2 a > [Shrink2 a] # enumFromTo :: Shrink2 a > Shrink2 a > [Shrink2 a] # enumFromThenTo :: Shrink2 a > Shrink2 a > Shrink2 a > [Shrink2 a] #  
Eq a => Eq (Shrink2 a) Source #  
Integral a => Integral (Shrink2 a) Source #  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Shrink2 a) Source #  
Defined in Test.QuickCheck.Modifiers  
Ord a => Ord (Shrink2 a) Source #  
Defined in Test.QuickCheck.Modifiers  
Read a => Read (Shrink2 a) Source #  
Real a => Real (Shrink2 a) Source #  
Defined in Test.QuickCheck.Modifiers toRational :: Shrink2 a > Rational #  
Show a => Show (Shrink2 a) Source #  
Arbitrary a => Arbitrary (Shrink2 a) Source #  
Shrinking _ x
: allows for maintaining a state during shrinking.
Shrinking s a 
class ShrinkState s a where Source #
shrinkInit :: a > s Source #
shrinkState :: a > s > [(a, s)] Source #
newtype ASCIIString Source #
ASCIIString
: generates an ASCII string.
Instances
newtype UnicodeString Source #
UnicodeString
: generates a unicode String.
The string will not contain surrogate pairs.
Instances
newtype PrintableString Source #
PrintableString
: generates a printable unicode String.
The string will not contain surrogate pairs.
Instances
Eq PrintableString Source #  
Defined in Test.QuickCheck.Modifiers (==) :: PrintableString > PrintableString > Bool # (/=) :: PrintableString > PrintableString > Bool #  
Ord PrintableString Source #  
Defined in Test.QuickCheck.Modifiers compare :: PrintableString > PrintableString > Ordering # (<) :: PrintableString > PrintableString > Bool # (<=) :: PrintableString > PrintableString > Bool # (>) :: PrintableString > PrintableString > Bool # (>=) :: PrintableString > PrintableString > Bool # max :: PrintableString > PrintableString > PrintableString # min :: PrintableString > PrintableString > PrintableString #  
Read PrintableString Source #  
Defined in Test.QuickCheck.Modifiers  
Show PrintableString Source #  
Defined in Test.QuickCheck.Modifiers showsPrec :: Int > PrintableString > ShowS # show :: PrintableString > String # showList :: [PrintableString] > ShowS #  
Arbitrary PrintableString Source #  
Defined in Test.QuickCheck.Modifiers 
Property combinators
The type of properties.
class Testable prop where Source #
The class of properties, i.e., types which QuickCheck knows how to test.
Typically a property will be a function returning Bool
or Property
.
If a property does no quantification, i.e. has no
parameters and doesn't use forAll
, it will only be tested once.
This may not be what you want if your property is an IO Bool
.
You can change this behaviour using the again
combinator.
property :: prop > Property Source #
Convert the thing to a property.
propertyForAllShrinkShow :: Gen a > (a > [a]) > (a > [String]) > (a > prop) > Property Source #
Optional; used internally in order to improve shrinking.
Tests a property but also quantifies over an extra value
(with a custom shrink and show function).
The Testable
instance for functions defines
propertyForAllShrinkShow
in a way that improves shrinking.
forAll :: (Show a, Testable prop) => Gen a > (a > prop) > Property Source #
Explicit universal quantification: uses an explicitly given test case generator.
forAllShrink :: (Show a, Testable prop) => Gen a > (a > [a]) > (a > prop) > Property Source #
Like forAll
, but tries to shrink the argument for failing test cases.
forAllShow :: Testable prop => Gen a > (a > String) > (a > prop) > Property Source #
Like forAll
, but with an explicitly given show function.
forAllShrinkShow :: Testable prop => Gen a > (a > [a]) > (a > String) > (a > prop) > Property Source #
Like forAllShrink
, but with an explicitly given show function.
forAllBlind :: Testable prop => Gen a > (a > prop) > Property Source #
Like forAll
, but without printing the generated value.
forAllShrinkBlind :: Testable prop => Gen a > (a > [a]) > (a > prop) > Property Source #
Like forAllShrink
, but without printing the generated value.
:: Testable prop  
=> (a > [a]) 

> a  The original argument 
> (a > prop)  
> Property 
Shrinks the argument to a property if it fails. Shrinking is done automatically for most types. This function is only needed when you want to override the default behavior.
(==>) :: Testable prop => Bool > prop > Property infixr 0 Source #
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. Note that using implication carelessly can
severely skew test case distribution: consider using cover
to make sure
that your test data is still good quality.
(===) :: (Eq a, Show a) => a > a > Property infix 4 Source #
Like ==
, but prints a counterexample when it fails.
(=/=) :: (Eq a, Show a) => a > a > Property infix 4 Source #
Like /=
, but prints a counterexample when it fails.
total :: NFData a => a > Property Source #
Checks that a value is total, i.e., doesn't crash when evaluated.
ioProperty :: Testable prop => IO prop > Property Source #
Do I/O inside a property.
Warning: any random values generated inside of the argument to ioProperty
will not currently be shrunk. For best results, generate all random values
before calling ioProperty
, or use idempotentIOProperty
if that is safe.
Note: if your property does no quantification, it will only be tested once.
To test it repeatedly, use again
.
idempotentIOProperty :: Testable prop => IO prop > Property Source #
Do I/O inside a property.
Warning: during shrinking, the I/O may not always be reexecuted.
Instead, the I/O may be executed once and then its result retained.
If this is not acceptable, use ioProperty
instead.
Controlling property execution
verbose :: Testable prop => prop > Property Source #
Prints out the generated test case every time the property is tested.
Only variables quantified over inside the verbose
are printed.
Note: for technical reasons, the test case is printed out after
the property is tested. To debug a property that goes into an
infinite loop, use within
to add a timeout instead.
verboseShrinking :: Testable prop => prop > Property Source #
Prints out the generated test case every time the property fails, including during shrinking.
Only variables quantified over inside the verboseShrinking
are printed.
Note: for technical reasons, the test case is printed out after
the property is tested. To debug a property that goes into an
infinite loop, use within
to add a timeout instead.
noShrinking :: Testable prop => prop > Property Source #
Disables shrinking for a property altogether.
Only quantification inside the call to noShrinking
is affected.
withMaxSuccess :: Testable prop => Int > prop > Property Source #
Configures how many times a property will be tested.
For example,
quickCheck (withMaxSuccess 1000 p)
will test p
up to 1000 times.
within :: Testable prop => Int > prop > Property Source #
Considers a property failed if it does not complete within the given number of microseconds.
Note: if the property times out, variables quantified inside the
within
will not be printed. Therefore, you should use within
only in the body of your property.
Good: prop_foo a b c = within 1000000 ...
Bad: prop_foo = within 1000000 $ \a b c > ...
Bad: prop_foo a b c = ...; main = quickCheck (within 1000000 prop_foo)
once :: Testable prop => prop > Property Source #
Modifies a property so that it only will be tested once.
Opposite of again
.
again :: Testable prop => prop > Property Source #
Modifies a property so that it will be tested repeatedly.
Opposite of once
.
mapSize :: Testable prop => (Int > Int) > prop > Property Source #
Adjust the test case size for a property, by transforming it with the given function.
Conjunction and disjunction
(.&.) :: (Testable prop1, Testable prop2) => prop1 > prop2 > Property infixr 1 Source #
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 Source #
Conjunction: p1
.&&.
p2
passes if both p1
and p2
pass.
(..) :: (Testable prop1, Testable prop2) => prop1 > prop2 > Property infixr 1 Source #
Disjunction: p1
..
p2
passes unless p1
and p2
simultaneously fail.
What to do on failure
counterexample :: Testable prop => String > prop > Property Source #
Adds the given string to the counterexample if the property fails.
printTestCase :: Testable prop => String > prop > Property Source #
Deprecated: Use counterexample instead
Adds the given string to the counterexample if the property fails.
whenFail :: Testable prop => IO () > prop > Property Source #
Performs an IO
action after the last failure of a property.
whenFail' :: Testable prop => IO () > prop > Property Source #
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 Source #
Indicates that a property is supposed to fail. QuickCheck will report an error if it does not fail.
Analysing test case distribution
label :: Testable prop => String > prop > Property Source #
Attaches a label to a test case. This is used for reporting test case distribution.
For example:
prop_reverse_reverse :: [Int] > Property prop_reverse_reverse xs = label ("length of input is " ++ show (length xs)) $ reverse (reverse xs) === xs
>>>
quickCheck prop_reverse_reverse
+++ OK, passed 100 tests: 7% length of input is 7 6% length of input is 3 5% length of input is 4 4% length of input is 6 ...
Each use of label
in your property results in a separate
table of test case distribution in the output. If this is
not what you want, use tabulate
.
collect :: (Show a, Testable prop) => a > prop > Property Source #
Attaches a label to a test case. This is used for reporting test case distribution.
collect x = label (show x)
For example:
prop_reverse_reverse :: [Int] > Property prop_reverse_reverse xs = collect (length xs) $ reverse (reverse xs) === xs
>>>
quickCheck prop_reverse_reverse
+++ OK, passed 100 tests: 7% 7 6% 3 5% 4 4% 6 ...
Each use of collect
in your property results in a separate
table of test case distribution in the output. If this is
not what you want, use tabulate
.
Reports how many test cases satisfy a given condition.
For example:
prop_sorted_sort :: [Int] > Property prop_sorted_sort xs = sorted xs ==> classify (length xs > 1) "nontrivial" $ sort xs === xs
>>>
quickCheck prop_sorted_sort
+++ OK, passed 100 tests (22% nontrivial).
tabulate :: Testable prop => String > [String] > prop > Property Source #
Collects information about test case distribution into a table.
The arguments to tabulate
are the table's name and a list of values
associated with the current test case. After testing, QuickCheck prints the
frequency of all collected values. The frequencies are expressed as a
percentage of the total number of values collected.
You should prefer tabulate
to label
when each test case is associated
with a varying number of values. Here is a (not terribly useful) example,
where the test data is a list of integers and we record all values that
occur in the list:
prop_sorted_sort :: [Int] > Property prop_sorted_sort xs = sorted xs ==> tabulate "List elements" (map show xs) $ sort xs === xs
>>>
quickCheck prop_sorted_sort
+++ OK, passed 100 tests; 1684 discarded. List elements (109 in total): 3.7% 0 3.7% 17 3.7% 2 3.7% 6 2.8% 6 2.8% 7
Here is a more useful example. We are testing a chatroom, where the user can log in, log out, or send a message:
data Command = LogIn  LogOut  SendMessage String deriving (Data, Show) instance Arbitrary Command where ...
There are some restrictions on command sequences; for example, the user must
log in before doing anything else. The function valid :: [Command] > Bool
checks that a command sequence is allowed. Our property then has the form:
prop_chatroom :: [Command] > Property prop_chatroom cmds = valid cmds ==> ...
The use of ==>
may skew test case distribution. We use collect
to see the
length of the command sequences, and tabulate
to get the frequencies of the
individual commands:
prop_chatroom :: [Command] > Property prop_chatroom cmds = wellFormed cmds LoggedOut ==> 'collect' (length cmds) $ 'tabulate' "Commands" (map (show . 'Data.Data.toConstr') cmds) $ ...
>>>
quickCheckWith stdArgs{maxDiscardRatio = 1000} prop_chatroom
+++ OK, passed 100 tests; 2775 discarded: 60% 0 20% 1 15% 2 3% 3 1% 4 1% 5 Commands (68 in total): 62% LogIn 22% SendMessage 16% LogOut
Checking test case distribution
:: Testable prop  
=> Double  The required percentage (0100) of test cases. 
> Bool 

> String  Label for the test case class. 
> prop  
> Property 
Checks that at least the given proportion of successful test cases belong to the given class. Discarded tests (i.e. ones with a false precondition) do not affect coverage.
Note: If the coverage check fails, QuickCheck prints out a warning, but
the property does not fail. To make the property fail, use checkCoverage
.
For example:
prop_sorted_sort :: [Int] > Property prop_sorted_sort xs = sorted xs ==> cover 50 (length xs > 1) "nontrivial" $ sort xs === xs
>>>
quickCheck prop_sorted_sort
+++ OK, passed 100 tests; 135 discarded (26% nontrivial). Only 26% nontrivial, but expected 50%
coverTable :: Testable prop => String > [(String, Double)] > prop > Property Source #
Checks that the values in a given table
appear a certain proportion of
the time. A call to coverTable
table
[(x1, p1), ..., (xn, pn)]
asserts
that of the values in table
, x1
should appear at least p1
percent of
the time, x2
at least p2
percent of the time, and so on.
Note: If the coverage check fails, QuickCheck prints out a warning, but
the property does not fail. To make the property fail, use checkCoverage
.
Continuing the example from the tabular
combinator...
data Command = LogIn  LogOut  SendMessage String deriving (Data, Show) prop_chatroom :: [Command] > Property prop_chatroom cmds = wellFormed cmds LoggedOut ==> 'tabulate' "Commands" (map (show . 'Data.Data.toConstr') cmds) $ ...
...we can add a coverage requirement as follows, which checks that LogIn
,
LogOut
and SendMessage
each occur at least 25% of the time:
prop_chatroom :: [Command] > Property prop_chatroom cmds = wellFormed cmds LoggedOut ==> coverTable "Commands" [("LogIn", 25), ("LogOut", 25), ("SendMessage", 25)] $ 'tabulate' "Commands" (map (show . 'Data.Data.toConstr') cmds) $ ... property goes here ...
>>>
quickCheck prop_chatroom
+++ OK, passed 100 tests; 2909 discarded: 56% 0 17% 1 10% 2 6% 3 5% 4 3% 5 3% 7 Commands (111 in total): 51.4% LogIn 30.6% SendMessage 18.0% LogOut Table 'Commands' had only 18.0% LogOut, but expected 25.0%
checkCoverage :: Testable prop => prop > Property Source #
Check that all coverage requirements defined by cover
and coverTable
are met, using a statistically sound test, and fail if they are not met.
Ordinarily, a failed coverage check does not cause the property to fail.
This is because the coverage requirement is not tested in a statistically
sound way. If you use cover
to express that a certain value must appear 20%
of the time, QuickCheck will warn you if the value only appears in 19 out of
100 test cases  but since the coverage varies randomly, you may have just
been unlucky, and there may not be any real problem with your test
generation.
When you use checkCoverage
, QuickCheck uses a statistical test to account
for the role of luck in coverage failures. It will run as many tests as
needed until it is sure about whether the coverage requirements are met. If a
coverage requirement is not met, the property fails.
Example:
quickCheck (checkCoverage prop_foo)
checkCoverageWith :: Testable prop => Confidence > prop > Property Source #
Check coverage requirements using a custom confidence level.
See stdConfidence
.
An example of making the statistical test less stringent in order to improve performance:
quickCheck (checkCoverageWith stdConfidence{certainty = 10^6} prop_foo)
data Confidence Source #
The statistical parameters used by checkCoverage
.
Confidence  

Instances
Show Confidence Source #  
Defined in Test.QuickCheck.State showsPrec :: Int > Confidence > ShowS # show :: Confidence > String # showList :: [Confidence] > ShowS # 
stdConfidence :: Confidence Source #
The standard parameters used by checkCoverage
: certainty = 10^9
,
tolerance = 0.9
. See Confidence
for the meaning of the parameters.
Generating example test cases
labelledExamples :: Testable prop => prop > IO () Source #
Given a property, which must use label
, collect
, classify
or cover
to associate labels with test cases, find an example test case for each possible label.
The example test cases are minimised using shrinking.
For example, suppose we test
and record the number
of times that delete
x xsx
occurs in xs
:
prop_delete :: Int > [Int] > Property prop_delete x xs = classify (count x xs == 0) "count x xs == 0" $ classify (count x xs == 1) "count x xs == 1" $ classify (count x xs >= 2) "count x xs >= 2" $ counterexample (show (delete x xs)) $ count x (delete x xs) == max 0 (count x xs1) where count x xs = length (filter (== x) xs)
labelledExamples
generates three example test cases, one for each label:
>>>
labelledExamples prop_delete
*** Found example of count x xs == 0 0 [] [] *** Found example of count x xs == 1 0 [0] [] *** Found example of count x xs >= 2 5 [5,5] [5] +++ OK, passed 100 tests: 78% count x xs == 0 21% count x xs == 1 1% count x xs >= 2
labelledExamplesWith :: Testable prop => Args > prop > IO () Source #
A variant of labelledExamples
that takes test arguments.
labelledExamplesWithResult :: Testable prop => Args > prop > IO Result Source #
A variant of labelledExamples
that takes test arguments and returns a result.
labelledExamplesResult :: Testable prop => prop > IO Result Source #
A variant of labelledExamples
that returns a result.