Test.QuickCheck.Property.Monad

Tutorial: http://github.com/bennofs/quickcheck-property-monad/tree/master/README.md

Note about the examples: The examples use a "-" in place of the empty line. This is required in order for doctest to work.

Documentation

data PropM a

PropM is a monad for writing properties that depend on random data. This is especially useful if you have many invariants for your data and cannot simply write an Arbitrary instance.

You can use a PropM a as a QuickCheck Testable if a is Testable. For example, you can use PropM Bool as a Testable property:

>>> quickCheck (return True :: PropM Bool)
+++ OK, passed 100 tests.

>>> quickCheck (return False :: PropM Bool)
*** Failed! Falsifiable (after 1 test):
-

Instances

Monad PropM

Functor PropM

Applicative PropM

Alternative PropM

MonadPlus PropM

Testable a => Testable (PropM a)

assert :: String -> Bool -> PropM ()

Assert that a certain condition is true. If the condition is false, fail with the given error message.

Examples:

>>> quickCheck $ assert "True is True!" True >> return True
+++ OK, passed 100 tests.

>>> quickCheck $ assert "False is True!" False >> return True
*** Failed! Falsifiable (after 1 test):
-
Assertion failed: False is True!

failWith :: String -> PropM ()

Fail with the given error message.

Example:

>>> quickCheck $ failWith "Something horrible happened" >> return True
*** Failed! Falsifiable (after 1 test):
-
Something horrible happened

gen :: Gen a -> PropM a

Use the given generator to generate a value.

Examples:

>>> quickCheck $ fmap (`elem` [0..5]) $ gen (elements [0..5])
+++ OK, passed 100 tests.

>>> quickCheck $ fmap (> 0) $ gen (choose (0,1))
*** Failed! Falsifiable (after 2 tests):
-

logMessage :: String -> PropM ()

Log a message that will be printed when the test case fails.

logMessageLn :: String -> PropM ()

Like logMessage but appends a line break after the message.

Example:

>>> quickCheck $ gen (choose (0,1)) >>= \x -> logMessageLn ("Chosen: " ++ show x) >> return (x > 0)
*** Failed! Falsifiable (after 2 tests):
Chosen: 0
-