AAA.txt

Using cabal to install quickcheck:

Make a directory to work in.
Inside the directory: “cabal sandbox init”
Then: “cabal install quickcheck”

You can open the GHCI repl in the sandbox:
"cabal repl"

And use normal commands like ":load filename.hs" 

To install hspec:
    cabal install hspec

To install tasty:
    cabal install tasty
    cabal install tasty-quickcheck
    cabal install tasty-hunit

arbitrary-instances.hs

{-# LANGUAGE InstanceSigs #-}

import Test.QuickCheck

-- you can run any of the 'sample' functions in GHCi
-- to print a list of examples

data Height = Height Int deriving (Show, Eq)

instance Arbitrary Height where
	arbitrary :: Gen Height 
	arbitrary = do
		height <- choose (100, 250)
		return (Height height)

sampleHeights :: IO [Height]
sampleHeights = sample' arbitrary

data Color = R | G | B	deriving (Eq, Show)

instance Arbitrary Color where
	arbitrary = do
		color <- frequency
			[(1, return R),
			(1, return G),
			(2, return B)]
		return color

sampleColors :: IO [Color]
sampleColors = sample' arbitrary

data Point = Point Int Int deriving (Eq, Show)

instance Arbitrary Point where

	arbitrary = do
		x <- arbitrary
		y <- arbitrary
		return (Point x y)

samplePoints :: IO [Point]
samplePoints = sample' arbitrary

HSpec-Tests.hs

import Test.Hspec
import Test.QuickCheck

-- https://hspec.github.io/

main = hspec $ do
	describe "Tests" $ do
		properties
		unitTests

properties = describe "List properties" $ do
	it "reverse . reverse == id" $
		property (\xs -> reverse (reverse xs) == (xs :: [Int]))

unitTests = describe "List tests" $ do
	it "List with one element is not empty" $ do
		not (null [1]) `shouldBe` True

	it "List with no elements is empty" $ do
		null [] `shouldBe` True

model-based.hs

import Test.QuickCheck

-- Operations on a queue:
class Queue q where
	push :: a -> q a -> q a
	pop :: q a -> q a

-- Implementation of a queue:
instance Queue [] where
	push x xs = 
		-- bug!
		if length xs == 12
		  then (x:x:xs)
		  else (x:xs)
	pop [] = []
	pop (x:xs) = xs

-- Our simplified model:
data QCount a = QCount { count :: Int } deriving Show

instance Queue QCount where
	push _ (QCount n) = QCount (n+1)
	pop (QCount 0) = QCount 0
	pop (QCount n) = QCount (n-1)

-- Actions on a queue:
data QueueAction a
	= Push a
	| Pop
	deriving (Show, Eq)

-- And we can generate arbitrary actions:
instance Arbitrary a => Arbitrary (QueueAction a) where
	arbitrary = do
		value <- arbitrary
		elements [Push value, Pop]

-- Apply an action to a queue:
act :: (Queue q) => QueueAction a -> q a -> q a
act (Push item) queue = push item queue
act (Pop) queue = pop queue

-- Apply a list of actions to the queue:
applyActions :: (Queue q) => q a -> [QueueAction a] -> q a
applyActions actions queue = foldr act actions queue

-- run "quickcheck checkAgainstModel"
checkAgainstModel :: [QueueAction Int] -> Property
checkAgainstModel actions = 
	length realQueue === count counterQueue
	where
		realQueue = applyActions [] actions
		counterQueue = applyActions (QCount 0) actions

name.hs

module Types (Name, toName) where

import Test.QuickCheck

newtype Name = Name String deriving (Eq, Ord, Show)

toName "" = Nothing
toName s = Just (Name s)

instance Arbitrary Name where

	arbitrary = do
		s <- listOf1 arbitrary
		case toName s of
			Nothing -> arbitrary
			Just name -> return name

UnitTests-Tasty.hs

import Test.Tasty
import Test.Tasty.QuickCheck
import Test.Tasty.HUnit

-- http://documentup.com/feuerbach/tasty

main = defaultMain tests

tests = testGroup "Tests" [properties, unitTests]

properties = testGroup "Properties" [
	testProperty "reverse . reverse == id" $
		\xs -> reverse (reverse xs) == (xs :: [Int])
	]

unitTests = testGroup "UnitTests" [
	testCase "List with one element is not empty" $
		True @=? not (null [1]),
	
	testCase "List with no elements is empty" $
		True @=? null []
	]