Test.QuickCheck.Property

Combinators for constructing properties.

Property and Testable types

newtype Property

The type of properties.

Backwards combatibility note: in older versions of QuickCheck Property was a type synonym for Gen Prop, so you could mix and match property combinators and Gen monad operations. Code that does this will no longer typecheck. However, it is easy to fix: because of the Testable typeclass, any combinator that expects a Property will also accept a Gen Property. If you have a Property where you need a Gen a, simply wrap the property combinator inside a return to get a Gen Property, and all should be well.

Constructors

MkProperty

Fields

unProperty :: Gen Prop

Instances

Testable Property

class Testable prop where

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

Minimal complete definition

property

Methods

property :: prop -> Property

Convert the thing to a property.

exhaustive :: prop -> Bool

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

Instances

Testable Bool

Testable Result

Testable Prop

Testable Discard

Testable Property

Testable prop => Testable (Gen prop)

(Arbitrary a, Show a, Testable prop) => Testable (a -> prop)

data Discard

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

Constructors

Discard

Instances

Testable Discard

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

Deprecated: Use ioProperty instead

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

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

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

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

Exception handling

protect :: (AnException -> a) -> IO a -> IO a

Type Prop

newtype Prop

Constructors

MkProp

Fields

unProp :: Rose Result

Instances

Testable Prop

type Rose

data Rose a

Constructors

MkRose a [Rose a]

IORose (IO (Rose a))

Instances

Monad Rose

Functor Rose

Applicative Rose

ioRose :: IO (Rose Result) -> Rose Result

joinRose :: Rose (Rose a) -> Rose a

reduceRose :: Rose Result -> IO (Rose Result)

Execute the IORose bits of a rose tree, returning a tree constructed by MkRose.

onRose :: (a -> [Rose a] -> Rose a) -> Rose a -> Rose a

Apply a function to the outermost MkRose constructor of a rose tree. The function must be total!

protectRose :: IO (Rose Result) -> IO (Rose Result)

Wrap a rose tree in an exception handler.

protectResults :: Rose Result -> Rose Result

Wrap all the Results in a rose tree in exception handlers.

Result type

data Callback

Different kinds of callbacks

Constructors

PostTest CallbackKind (State -> Result -> IO ())

Called just after a test

PostFinalFailure CallbackKind (State -> Result -> IO ())

Called with the final failing test-case

data CallbackKind

Constructors

Counterexample

Affected by the verbose combinator

NotCounterexample

Not affected by the verbose combinator

data Result

The result of a single test.

Constructors

MkResult

Fields

ok :: Maybe Bool

result of the test case; Nothing = discard

expect :: Bool

indicates what the expected result of the property is

reason :: String

a message indicating what went wrong

theException :: Maybe AnException

the exception thrown, if any

abort :: Bool

if True, the test should not be repeated

labels :: Map String Int

all labels used by this property

stamp :: Set String

the collected values for this test case

callbacks :: [Callback]

the callbacks for this test case

Instances

Testable Result

exception :: String -> AnException -> Result

formatException :: String -> AnException -> String

protectResult :: IO Result -> IO Result

succeeded :: Result

failed :: Result

rejected :: Result

Lifting and mapping functions

liftBool :: Bool -> Result

mapResult :: Testable prop => (Result -> Result) -> prop -> Property

mapTotalResult :: Testable prop => (Result -> Result) -> prop -> Property

mapRoseResult :: Testable prop => (Rose Result -> Rose Result) -> prop -> Property

mapProp :: Testable prop => (Prop -> Prop) -> prop -> Property

Property combinators

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

Changes the maximum test case size for a property.

shrinking

Arguments

:: Testable prop

=> (a -> [a])

shrink-like function.

-> a

The original argument

-> (a -> prop)

-> Property

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

noShrinking :: Testable prop => prop -> Property

Disables shrinking for a property altogether.

callback :: Testable prop => Callback -> prop -> Property

Adds a callback

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

Adds the given string to the counterexample.

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

Deprecated: Use counterexample instead

Adds the given string to the counterexample.

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

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

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

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

verbose :: Testable prop => prop -> Property

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

expectFailure :: Testable prop => prop -> Property

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

once :: Testable prop => prop -> Property

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

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

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

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

Labels a property with a value:

collect x = label (show x)

classify

Arguments

:: Testable prop

=> Bool

True if the test case should be labelled.

-> String

Label.

-> prop

-> Property

Conditionally labels test case.

cover

Arguments

:: Testable prop

=> Bool

True if the test case belongs to the class.

-> Int

The required percentage (0-100) of test cases.

-> String

Label for the test case class.

-> prop

-> Property

Checks that at least the given proportion of successful test cases belong to the given class. Discarded tests (i.e. ones with a false precondition) do not affect coverage.

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

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

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

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

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

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

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

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

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

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

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

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

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

Take the conjunction of several properties.

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

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

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

Take the disjunction of several properties.

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

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