Testing monoid subclass instances with QuickCheck.

QuickCheck support for testing instances of type classes defined in the monoid-subclasses library.

quickcheck-monoid-subclasses

Overview

The quickcheck-monoid-subclasses library provides:

• QuickCheck support for testing instances of type classes defined in the monoid-subclasses library.
• Compatibility with the quickcheck-classes library.
• Reusable properties for type class laws, in the form of Laws definitions.

Usage

In general, usage is identical to that of the quickcheck-classes library. If you're already familiar with quickcheck-classes, then using this library should be straightforward.

Testing laws for a single type class

To test that the laws of a particular class hold for a particular type, use the lawsCheck function with the Laws definition for the class you wish to test.

:stars: Example

To test that the Monus laws hold for the SumNatural type:

import Data.Monoid (Sum)
import Data.Proxy (Proxy (Proxy))
import Numeric.Natural (Natural)
import Test.QuickCheck.Classes (lawsCheck)
import Test.QuickCheck.Classes.Monoid.Monus (monusLaws)

lawsCheck (monusLaws (Proxy :: Proxy (Sum Natural)))

If all tests pass, you should see output similar to:

Monus: axiom1 +++ OK, passed 100 tests.
Monus: axiom2 +++ OK, passed 100 tests.
Monus: axiom3 +++ OK, passed 100 tests.
Monus: axiom4 +++ OK, passed 100 tests.
Monus: stripPrefixOverlap +++ OK, passed 100 tests.
Monus: stripSuffixOverlap +++ OK, passed 100 tests.

Testing laws for multiple type classes

To test that the laws of multiple classes hold for a particular type, use the lawsCheckOne function with the Laws definitions for the classes you wish to test.

:stars: Example

To test that the SumNatural type satisfies the laws of Semigroup and its subclasses:

import Data.Monoid (Sum)
import Data.Proxy (Proxy (Proxy))
import Numeric.Natural (Natural)
import Test.QuickCheck.Classes
import Test.QuickCheck.Classes.Monoid.GCD
import Test.QuickCheck.Classes.Monoid.LCM
import Test.QuickCheck.Classes.Monoid.Monus
import Test.QuickCheck.Classes.Monoid.Null
import Test.QuickCheck.Classes.Semigroup.Cancellative
import Test.QuickCheck.Classes.Semigroup.Factorial

lawsCheckOne (Proxy :: Proxy (Sum Natural))
    [ cancellativeLaws
    , commutativeLaws
    , distributiveGCDMonoidLaws
    , distributiveLCMMonoidLaws
    , factorialLaws
    , factorialMonoidLaws
    , gcdMonoidLaws
    , lcmMonoidLaws
    , leftCancellativeLaws
    , leftDistributiveGCDMonoidLaws
    , leftGCDMonoidLaws
    , leftReductiveLaws
    , monoidLaws
    , monoidNullLaws
    , monusLaws
    , overlappingGCDMonoidLaws
    , positiveMonoidLaws
    , reductiveLaws
    , rightCancellativeLaws
    , rightDistributiveGCDMonoidLaws
    , rightGCDMonoidLaws
    , rightReductiveLaws
    , semigroupLaws
    , stableFactorialLaws
    ]

Subclasses and superclasses

Each of the Laws definitions provided by this library corresponds to exactly one type class, and includes just the laws for that class. Laws for subclasses and superclasses are not automatically included. Therefore, you'll need to explicitly test the laws of every single class you wish to cover.

Coverage checks

This library includes coverage checks to ensure that important cases are covered, and to reduce the probability of test passes that are false positives. These coverage checks are performed automatically.

To increase coverage of interesting and important cases, this library also checks that laws hold for combinations of generated arbitrary values.

:stars: Example

Suppose we are testing the following law:

isPrefixOf a b == isJust (stripPrefix a b)

This library will also test that the following derived laws hold:

isPrefixOf a (a <> a) == isJust (stripPrefix a (a <> a))
isPrefixOf a (a <> b) == isJust (stripPrefix a (a <> b))
isPrefixOf a (b <> a) == isJust (stripPrefix a (b <> a))