Safe Haskell  Safe 

Language  Haskell2010 
This module implements a simplified, pure version of Test.Quickcheck's quickCheck functionality.
Synopsis
 quickCheck :: STestable prop => QCGen > prop > String
 quickCheckResult :: STestable prop => QCGen > prop > Result
 quickCheckWith :: STestable prop => Args > QCGen > prop > String
 quickCheckWithResult :: STestable prop => Args > QCGen > prop > Result
 class STestable prop
 (==>) :: STestable prop => Bool > prop > SProperty
 (..) :: (STestable prop2, STestable prop1) => prop1 > prop2 > SProperty
 (.&&.) :: (STestable prop2, STestable prop1) => prop1 > prop2 > SProperty
 (.&.) :: (STestable prop2, STestable prop1) => prop1 > prop2 > SProperty
 (===) :: (Eq a, Show a) => a > a > SProperty
 label :: STestable prop => String > prop > SProperty
 shrinking :: STestable prop => (a > [a]) > a > (a > prop) > SProperty
 noShrinking :: STestable prop => prop > SProperty
 mapSize :: STestable prop => (Int > Int) > prop > SProperty
 forAll :: (Show a, STestable prop) => Gen a > (a > prop) > SProperty
 forAllShrink :: (Show a, STestable prop) => Gen a > (a > [a]) > (a > prop) > SProperty
 inventQCGen :: a > QCGen
 labelledExamplesWithResult :: Testable prop => Args > prop > IO Result
 labelledExamplesResult :: Testable prop => prop > IO Result
 labelledExamplesWith :: Testable prop => Args > prop > IO ()
 labelledExamples :: Testable prop => prop > IO ()
 verboseCheckAll :: Q Exp
 quickCheckAll :: Q Exp
 allProperties :: Q Exp
 forAllProperties :: Q Exp
 monomorphic :: Name > ExpQ
 polyVerboseCheck :: Name > ExpQ
 polyQuickCheck :: Name > ExpQ
 verboseCheckWithResult :: Testable prop => Args > prop > IO Result
 verboseCheckResult :: Testable prop => prop > IO Result
 verboseCheckWith :: Testable prop => Args > prop > IO ()
 verboseCheck :: Testable prop => prop > IO ()
 stdArgs :: Args
 isSuccess :: Result > Bool
 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 { }
 total :: NFData a => a > Property
 (=/=) :: (Eq a, Show a) => a > a > Property
 forAllShrinkBlind :: Testable prop => Gen a > (a > [a]) > (a > prop) > Property
 forAllShrinkShow :: Testable prop => Gen a > (a > [a]) > (a > String) > (a > prop) > Property
 forAllBlind :: Testable prop => Gen a > (a > prop) > Property
 forAllShow :: Testable prop => Gen a > (a > String) > (a > prop) > Property
 coverTable :: Testable prop => String > [(String, Double)] > prop > Property
 tabulate :: Testable prop => String > [String] > prop > Property
 stdConfidence :: Confidence
 checkCoverageWith :: Testable prop => Confidence > prop > Property
 checkCoverage :: Testable prop => prop > Property
 withMaxSuccess :: Testable prop => Int > prop > Property
 again :: Testable prop => prop > Property
 verboseShrinking :: Testable prop => prop > Property
 whenFail' :: Testable prop => IO () > prop > Property
 whenFail :: Testable prop => IO () > prop > Property
 idempotentIOProperty :: Testable prop => IO prop > Property
 ioProperty :: Testable prop => IO prop > Property
 data Discard = Discard
 data Confidence = Confidence {}
 applyFun3 :: Fun (a, b, c) d > a > b > c > d
 applyFun2 :: Fun (a, b) c > a > b > c
 applyFun :: Fun a b > a > b
 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
 pattern Fn :: forall a b. (a > b) > Fun a b
 pattern Fn2 :: forall a b c. (a > b > c) > Fun (a, b) c
 pattern Fn3 :: forall a b c d. (a > b > c > d) > Fun (a, b, c) d
 class Function a where
 data Fun a b = Fun (a :> b, b, Shrunk) (a > b)
 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
 newtype Shrink2 a = Shrink2 {
 getShrink2 :: a
 data Smart a = Smart Int 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 {}
 infiniteList :: Arbitrary a => Gen [a]
 orderedList :: (Ord a, Arbitrary a) => Gen [a]
 vector :: Arbitrary a => Int > Gen [a]
 coarbitraryEnum :: Enum a => a > Gen b > Gen b
 coarbitraryShow :: Show a => a > Gen b > Gen b
 coarbitraryReal :: Real a => a > Gen b > Gen b
 coarbitraryIntegral :: Integral a => a > Gen b > Gen b
 (><) :: (Gen a > Gen a) > (Gen a > Gen a) > Gen a > Gen a
 genericCoarbitrary :: (Generic a, GCoArbitrary (Rep a)) => a > Gen b > Gen b
 shrinkDecimal :: RealFrac a => a > [a]
 shrinkRealFrac :: RealFrac a => a > [a]
 shrinkIntegral :: Integral a => a > [a]
 shrinkMapBy :: (a > b) > (b > a) > (a > [a]) > b > [b]
 shrinkMap :: Arbitrary a => (a > b) > (b > a) > b > [b]
 shrinkNothing :: a > [a]
 arbitraryPrintableChar :: Gen Char
 arbitraryASCIIChar :: Gen Char
 arbitraryUnicodeChar :: Gen Char
 arbitrarySizedBoundedIntegral :: (Bounded a, Integral a) => Gen a
 arbitraryBoundedEnum :: (Bounded a, Enum a) => Gen a
 arbitraryBoundedRandom :: (Bounded a, Random a) => Gen a
 arbitraryBoundedIntegral :: (Bounded a, Integral a) => Gen a
 arbitrarySizedFractional :: Fractional a => Gen a
 arbitrarySizedNatural :: Integral a => Gen a
 arbitrarySizedIntegral :: Integral a => Gen a
 applyArbitrary4 :: (Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d) => (a > b > c > d > r) > Gen r
 applyArbitrary3 :: (Arbitrary a, Arbitrary b, Arbitrary c) => (a > b > c > r) > Gen r
 applyArbitrary2 :: (Arbitrary a, Arbitrary b) => (a > b > r) > Gen r
 shrinkList :: (a > [a]) > [a] > [[a]]
 subterms :: (Generic a, GSubterms (Rep a) a) => a > [a]
 recursivelyShrink :: (Generic a, RecursivelyShrink (Rep a)) => a > [a]
 genericShrink :: (Generic a, RecursivelyShrink (Rep a), GSubterms (Rep a) a) => a > [a]
 shrink2 :: (Arbitrary2 f, Arbitrary a, Arbitrary b) => f a b > [f a b]
 arbitrary2 :: (Arbitrary2 f, Arbitrary a, Arbitrary b) => Gen (f a b)
 shrink1 :: (Arbitrary1 f, Arbitrary a) => f a > [f a]
 arbitrary1 :: (Arbitrary1 f, Arbitrary a) => Gen (f a)
 class Arbitrary a where
 class Arbitrary1 (f :: Type > Type) where
 liftArbitrary :: Gen a > Gen (f a)
 liftShrink :: (a > [a]) > f a > [f a]
 class Arbitrary2 (f :: Type > Type > Type) where
 liftArbitrary2 :: Gen a > Gen b > Gen (f a b)
 liftShrink2 :: (a > [a]) > (b > [b]) > f a b > [f a b]
 class CoArbitrary a where
 coarbitrary :: a > Gen b > Gen b
 infiniteListOf :: Gen a > Gen [a]
 vectorOf :: Int > Gen a > Gen [a]
 listOf1 :: Gen a > Gen [a]
 listOf :: Gen a > Gen [a]
 growingElements :: [a] > Gen a
 shuffle :: [a] > Gen [a]
 sublistOf :: [a] > Gen [a]
 elements :: [a] > Gen a
 frequency :: [(Int, Gen a)] > Gen a
 oneof :: [Gen a] > Gen a
 suchThatMaybe :: Gen a > (a > Bool) > Gen (Maybe a)
 suchThatMap :: Gen a > (a > Maybe b) > Gen b
 suchThat :: Gen a > (a > Bool) > Gen a
 sample :: Show a => Gen a > IO ()
 sample' :: Gen a > IO [a]
 generate :: Gen a > IO a
 choose :: Random a => (a, a) > Gen a
 scale :: (Int > Int) > Gen a > Gen a
 resize :: Int > Gen a > Gen a
 getSize :: Gen Int
 sized :: (Int > Gen a) > Gen a
 variant :: Integral n => n > Gen a > Gen a
 data Gen a
 discard :: a
Checking properties
quickCheck :: STestable prop => QCGen > prop > String Source #
Cf. quickCheck
. Note that in contrast to QuickCheck's
function, this one takes an additional QCGen
argument.
>>>
putStr $ quickCheck (inventQCGen ()) (\x > length (x :: [()]) < 10)
*** Failed! Falsifiable (after 18 tests and 3 shrinks): [(),(),(),(),(),(),(),(),(),(),(),(),(),(),()]
quickCheckResult :: STestable prop => QCGen > prop > Result Source #
Cf. quickCheckResult
. Note that in contrast to
QuickCheck's function, this one takes an additional QCGen
argument.
quickCheckWith :: STestable prop => Args > QCGen > prop > String Source #
Cf. quickCheckWith
. Note that in contrast to
QuickCheck's function, this one takes an additional QCGen
argument.
quickCheckWithResult :: STestable prop => Args > QCGen > prop > Result Source #
Cf. quickCheckWithResult
. Note that in contrast to
QuickCheck's function, this one takes an additional QCGen
argument.
Creating and combining properties
sProperty
(..) :: (STestable prop2, STestable prop1) => prop1 > prop2 > SProperty Source #
Disjunction. Cf. ..
.
(.&&.) :: (STestable prop2, STestable prop1) => prop1 > prop2 > SProperty Source #
Conjunction. Cf. .&&.
.
(.&.) :: (STestable prop2, STestable prop1) => prop1 > prop2 > SProperty Source #
Nondeterministic conjunction. Cf. &.
.
shrinking :: STestable prop => (a > [a]) > a > (a > prop) > SProperty Source #
Shrink counterexamples. Cf. shrinking
.
noShrinking :: STestable prop => prop > SProperty Source #
Suppress shrinking of counterexamples. Cf. noShrinking
.
mapSize :: STestable prop => (Int > Int) > prop > SProperty Source #
Adjust testcase sizes. Cf. mapSize
.
forAll :: (Show a, STestable prop) => Gen a > (a > prop) > SProperty Source #
Universal quantification. Cf. forAll
.
forAllShrink :: (Show a, STestable prop) => Gen a > (a > [a]) > (a > prop) > SProperty Source #
Universal quantification with shrinking.
Cf. forAllShrink
.
Miscellaneous
inventQCGen :: a > QCGen Source #
inventQCGen
invokes newQCGen
via
unsafePerformIO
. It is useful in connection with the
quickCheck
family of functions.
labelledExamplesWithResult :: Testable prop => Args > prop > IO Result #
A variant of labelledExamples
that takes test arguments and returns a result.
labelledExamplesResult :: Testable prop => prop > IO Result #
A variant of labelledExamples
that returns a result.
labelledExamplesWith :: Testable prop => Args > prop > IO () #
A variant of labelledExamples
that takes test arguments.
labelledExamples :: Testable prop => prop > IO () #
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
verboseCheckAll :: Q Exp #
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 []
.
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.
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!
allProperties :: Q Exp #
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 []
.
forAllProperties :: Q Exp #
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 []
.
monomorphic :: Name > ExpQ #
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 []
.
polyVerboseCheck :: Name > ExpQ #
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 []
.
polyQuickCheck :: Name > ExpQ #
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 []
.
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
.
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
.
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
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 

total :: NFData a => a > Property #
Checks that a value is total, i.e., doesn't crash when evaluated.
(=/=) :: (Eq a, Show a) => a > a > Property infix 4 #
Like /=
, but prints a counterexample when it fails.
forAllShrinkBlind :: Testable prop => Gen a > (a > [a]) > (a > prop) > Property #
Like forAllShrink
, but without printing the generated value.
forAllShrinkShow :: Testable prop => Gen a > (a > [a]) > (a > String) > (a > prop) > Property #
Like forAllShrink
, but with an explicitly given show function.
forAllBlind :: Testable prop => Gen a > (a > prop) > Property #
Like forAll
, but without printing the generated value.
forAllShow :: Testable prop => Gen a > (a > String) > (a > prop) > Property #
Like forAll
, but with an explicitly given show function.
coverTable :: Testable prop => String > [(String, Double)] > prop > Property #
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%
tabulate :: Testable prop => String > [String] > prop > Property #
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
The standard parameters used by checkCoverage
: certainty = 10^9
,
tolerance = 0.9
. See Confidence
for the meaning of the parameters.
checkCoverageWith :: Testable prop => Confidence > prop > Property #
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)
checkCoverage :: Testable prop => prop > Property #
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)
withMaxSuccess :: Testable prop => Int > prop > Property #
Configures how many times a property will be tested.
For example,
quickCheck (withMaxSuccess 1000 p)
will test p
up to 1000 times.
again :: Testable prop => prop > Property #
Modifies a property so that it will be tested repeatedly.
Opposite of once
.
verboseShrinking :: Testable prop => prop > Property #
Prints out the generated testcase every time the property fails, including during shrinking.
Only variables quantified over inside the verboseShrinking
are printed.
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.
whenFail :: Testable prop => IO () > prop > Property #
Performs an IO
action after the last failure of a property.
idempotentIOProperty :: Testable prop => IO prop > Property #
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.
ioProperty :: Testable prop => IO prop > Property #
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
.
data Confidence #
The statistical parameters used by checkCoverage
.
Confidence  

Instances
Show Confidence  
Defined in Test.QuickCheck.State showsPrec :: Int > Confidence > ShowS # show :: Confidence > String # showList :: [Confidence] > ShowS # 
applyFun3 :: Fun (a, b, c) d > a > b > c > d #
Extracts the value of a ternary function. Fn3
is the
pattern equivalent of this function.
applyFun2 :: Fun (a, b) c > a > b > c #
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]
applyFun :: Fun a b > a > b #
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"
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 #
pattern Fn :: forall a b. (a > b) > Fun a b #
A modifier for testing functions.
prop :: Fun String Integer > Bool prop (Fn f) = f "banana" == f "monkey"  f "banana" == f "elephant"
pattern Fn2 :: forall a b c. (a > b > c) > Fun (a, b) c #
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 :: forall a b c d. (a > b > c > d) > Fun (a, b, c) d #
A modifier for testing ternary functions.
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
Generation of random shrinkable, showable functions.
To generate random values of type
,
you must have an instance Fun
a b
.Function
a
Blind x
: as x, but x does not have to be in the Show
class.
Instances
Functor Blind  
Enum a => Enum (Blind a)  
Eq a => Eq (Blind a)  
Integral a => Integral (Blind a)  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Blind a)  
Ord a => Ord (Blind a)  
Real a => Real (Blind a)  
Defined in Test.QuickCheck.Modifiers toRational :: Blind a > Rational #  
Show (Blind a)  
Arbitrary a => Arbitrary (Blind a)  
Fixed x
: as x, but will not be shrunk.
Instances
Functor Fixed  
Enum a => Enum (Fixed a)  
Eq a => Eq (Fixed a)  
Integral a => Integral (Fixed a)  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Fixed a)  
Ord a => Ord (Fixed a)  
Read a => Read (Fixed a)  
Real a => Real (Fixed a)  
Defined in Test.QuickCheck.Modifiers toRational :: Fixed a > Rational #  
Show a => Show (Fixed a)  
Arbitrary a => Arbitrary (Fixed a)  
newtype OrderedList a #
Ordered xs
: guarantees that xs is ordered.
Ordered  

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

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

Instances
Functor Positive  
Enum a => Enum (Positive a)  
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)  
Ord a => Ord (Positive a)  
Read a => Read (Positive a)  
Show a => Show (Positive a)  
(Num a, Ord a, Arbitrary a) => Arbitrary (Positive a)  
Negative x
: guarantees that x < 0
.
Negative  

Instances
Functor Negative  
Enum a => Enum (Negative a)  
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)  
Ord a => Ord (Negative a)  
Read a => Read (Negative a)  
Show a => Show (Negative a)  
(Num a, Ord a, Arbitrary a) => Arbitrary (Negative a)  
NonZero x
: guarantees that x /= 0
.
NonZero  

Instances
Functor NonZero  
Enum a => Enum (NonZero a)  
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)  
Ord a => Ord (NonZero a)  
Defined in Test.QuickCheck.Modifiers  
Read a => Read (NonZero a)  
Show a => Show (NonZero a)  
(Num a, Eq a, Arbitrary a) => Arbitrary (NonZero a)  
newtype NonNegative a #
NonNegative x
: guarantees that x >= 0
.
Instances
newtype NonPositive a #
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  
Enum a => Enum (Large a)  
Eq a => Eq (Large a)  
Integral a => Integral (Large a)  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Large a)  
Ord a => Ord (Large a)  
Read a => Read (Large a)  
Real a => Real (Large a)  
Defined in Test.QuickCheck.Modifiers toRational :: Large a > Rational #  
Show a => Show (Large a)  
Ix a => Ix (Large a)  
Defined in Test.QuickCheck.Modifiers  
(Integral a, Bounded a) => Arbitrary (Large a)  
Small x
: generates values of x
drawn from a small range.
The opposite of Large
.
Instances
Functor Small  
Enum a => Enum (Small a)  
Eq a => Eq (Small a)  
Integral a => Integral (Small a)  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Small a)  
Ord a => Ord (Small a)  
Read a => Read (Small a)  
Real a => Real (Small a)  
Defined in Test.QuickCheck.Modifiers toRational :: Small a > Rational #  
Show a => Show (Small a)  
Ix a => Ix (Small a)  
Defined in Test.QuickCheck.Modifiers  
Integral a => Arbitrary (Small a)  
Shrink2 x
: allows 2 shrinking steps at the same time when shrinking x
Shrink2  

Instances
Functor Shrink2  
Enum a => Enum (Shrink2 a)  
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)  
Integral a => Integral (Shrink2 a)  
Defined in Test.QuickCheck.Modifiers  
Num a => Num (Shrink2 a)  
Defined in Test.QuickCheck.Modifiers  
Ord a => Ord (Shrink2 a)  
Defined in Test.QuickCheck.Modifiers  
Read a => Read (Shrink2 a)  
Real a => Real (Shrink2 a)  
Defined in Test.QuickCheck.Modifiers toRational :: Shrink2 a > Rational #  
Show a => Show (Shrink2 a)  
Arbitrary a => Arbitrary (Shrink2 a)  
Smart _ x
: tries a different order when shrinking.
Shrinking _ x
: allows for maintaining a state during shrinking.
Shrinking s a 
class ShrinkState s a where #
shrinkInit :: a > s #
shrinkState :: a > s > [(a, s)] #
newtype ASCIIString #
ASCIIString
: generates an ASCII string.
Instances
newtype UnicodeString #
UnicodeString
: generates a unicode String.
The string will not contain surrogate pairs.
Instances
newtype PrintableString #
PrintableString
: generates a printable unicode String.
The string will not contain surrogate pairs.
Instances
Eq PrintableString  
Defined in Test.QuickCheck.Modifiers (==) :: PrintableString > PrintableString > Bool # (/=) :: PrintableString > PrintableString > Bool #  
Ord PrintableString  
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  
Defined in Test.QuickCheck.Modifiers  
Show PrintableString  
Defined in Test.QuickCheck.Modifiers showsPrec :: Int > PrintableString > ShowS # show :: PrintableString > String # showList :: [PrintableString] > ShowS #  
Arbitrary PrintableString  
Defined in Test.QuickCheck.Modifiers arbitrary :: Gen PrintableString # shrink :: PrintableString > [PrintableString] # 
infiniteList :: Arbitrary a => Gen [a] #
Generates an infinite list.
orderedList :: (Ord a, Arbitrary a) => Gen [a] #
Generates an ordered list.
coarbitraryEnum :: Enum a => a > Gen b > Gen b #
A coarbitrary
implementation for enums.
coarbitraryShow :: Show a => a > Gen b > Gen b #
coarbitrary
helper for lazy people :).
coarbitraryReal :: Real a => a > Gen b > Gen b #
A coarbitrary
implementation for real numbers.
coarbitraryIntegral :: Integral a => a > Gen b > Gen b #
A coarbitrary
implementation for integral numbers.
(><) :: (Gen a > Gen a) > (Gen a > Gen a) > Gen a > Gen a #
Combine two generator perturbing functions, for example the
results of calls to variant
or coarbitrary
.
genericCoarbitrary :: (Generic a, GCoArbitrary (Rep a)) => a > Gen b > Gen b #
Generic CoArbitrary implementation.
shrinkDecimal :: RealFrac a => a > [a] #
Shrink a real number, preferring numbers with shorter
decimal representations. See also shrinkRealFrac
.
shrinkRealFrac :: RealFrac a => a > [a] #
Shrink a fraction, preferring numbers with smaller
numerators or denominators. See also shrinkDecimal
.
shrinkIntegral :: Integral a => a > [a] #
Shrink an integral number.
shrinkMapBy :: (a > b) > (b > a) > (a > [a]) > b > [b] #
Nonoverloaded version of shrinkMap
.
shrinkMap :: Arbitrary a => (a > b) > (b > a) > b > [b] #
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
shrinkNothing :: a > [a] #
Returns no shrinking alternatives.
arbitraryPrintableChar :: Gen Char #
Generates a printable Unicode character.
arbitraryASCIIChar :: Gen Char #
Generates a random ASCII character (0127).
arbitraryUnicodeChar :: Gen Char #
Generates any Unicode character (but not a surrogate)
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.
arbitraryBoundedEnum :: (Bounded a, Enum a) => Gen a #
Generates an element of a bounded enumeration.
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.
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.
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.
arbitrarySizedNatural :: Integral a => Gen a #
Generates a natural number. The number's maximum value depends on the size parameter.
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.
applyArbitrary4 :: (Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d) => (a > b > c > d > r) > Gen r #
Apply a function of arity 4 to random arguments.
applyArbitrary3 :: (Arbitrary a, Arbitrary b, Arbitrary c) => (a > b > c > r) > Gen r #
Apply a ternary function to random arguments.
applyArbitrary2 :: (Arbitrary a, Arbitrary b) => (a > b > r) > Gen r #
Apply a binary function to random arguments.
shrinkList :: (a > [a]) > [a] > [[a]] #
Shrink a list of values given a shrinking function for individual values.
recursivelyShrink :: (Generic a, RecursivelyShrink (Rep a)) => a > [a] #
Recursively shrink all immediate subterms.
genericShrink :: (Generic a, RecursivelyShrink (Rep a), GSubterms (Rep a) a) => a > [a] #
Shrink a term to any of its immediate subterms, and also recursively shrink all subterms.
shrink2 :: (Arbitrary2 f, Arbitrary a, Arbitrary b) => f a b > [f a b] #
arbitrary2 :: (Arbitrary2 f, Arbitrary a, Arbitrary b) => Gen (f a b) #
shrink1 :: (Arbitrary1 f, Arbitrary a) => f a > [f a] #
arbitrary1 :: (Arbitrary1 f, Arbitrary a) => Gen (f a) #
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
class Arbitrary1 (f :: Type > Type) where #
Lifting of the Arbitrary
class to unary type constructors.
liftArbitrary :: Gen a > Gen (f a) #
liftShrink :: (a > [a]) > f a > [f a] #
Instances
class Arbitrary2 (f :: Type > Type > Type) where #
Lifting of the Arbitrary
class to binary type constructors.
liftArbitrary2 :: Gen a > Gen b > Gen (f a b) #
liftShrink2 :: (a > [a]) > (b > [b]) > f a b > [f a b] #
Instances
Arbitrary2 Either  
Defined in Test.QuickCheck.Arbitrary liftArbitrary2 :: Gen a > Gen b > Gen (Either a b) # liftShrink2 :: (a > [a]) > (b > [b]) > Either a b > [Either a b] #  
Arbitrary2 (,)  
Defined in Test.QuickCheck.Arbitrary liftArbitrary2 :: Gen a > Gen b > Gen (a, b) # liftShrink2 :: (a > [a]) > (b > [b]) > (a, b) > [(a, b)] #  
Arbitrary2 (Const :: Type > Type > Type)  
Defined in Test.QuickCheck.Arbitrary liftArbitrary2 :: Gen a > Gen b > Gen (Const a b) # liftShrink2 :: (a > [a]) > (b > [b]) > Const a b > [Const a b] #  
Arbitrary2 (Constant :: Type > Type > Type)  
Defined in Test.QuickCheck.Arbitrary liftArbitrary2 :: Gen a > Gen b > Gen (Constant a b) # liftShrink2 :: (a > [a]) > (b > [b]) > Constant a b > [Constant a b] # 
class CoArbitrary a where #
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 #
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
infiniteListOf :: Gen a > Gen [a] #
Generates an infinite list.
Generates a nonempty list of random length. The maximum length depends on the size parameter.
Generates a list of random length. The maximum length depends on the size parameter.
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 nonempty.
frequency :: [(Int, Gen a)] > Gen a #
Chooses one of the given generators, with a weighted random distribution. The input list must be nonempty.
Randomly uses one of the given generators. The input list must be nonempty.
suchThatMaybe :: Gen a > (a > Bool) > Gen (Maybe a) #
Tries to generate a value that satisfies a predicate.
If it fails to do so after enough attempts, returns Nothing
.
suchThatMap :: Gen a > (a > Maybe b) > Gen b #
Generates a value for which the given function returns a Just
, and then
applies the function.
Run a generator. The size passed to the generator is always 30;
if you want another size then you should explicitly use resize
.
scale :: (Int > Int) > Gen a > Gen a #
Adjust the size parameter, by transforming it with the given function.
resize :: Int > Gen a > Gen a #
Overrides the size parameter. Returns a generator which uses the given size instead of the runtimesize parameter.
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
.
sized :: (Int > Gen a) > Gen a #
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
.
A generator for values of type a
.
The thirdparty packages
QuickCheckGenT
and
quickchecktransformer
provide monad transformer versions of Gen
.