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FsCheck.Properties
This repository contains some basic Property Functions.
Some examples:
Idempotent
The result of a function stays the same after running the function multiple times.
/// Defines extensional equality. This allows concise, point-free, definitions of laws.
/// f(x) == g(x)
/// f <=> g
let (.=.) x y = x = y |@ sprintf "%A = %A" x y
let (<=>) f g x = f x .=. g x
/// Checks whether a function is idempotent.
/// f(f(x)) == f(x)
/// quickCheck $ idempotent (abs :: Int -> Int)
let idempotent f = f <=> (f >> f)Can be tested as:
[<Property>]
let ``Idempotent Property`` i =
idempotent abs iInverts
One function is the inverse of another function.
/// Checks whether a function is the inverse of another function.
/// f(g(x)) = x
/// quickCheck $ (`div` 2) `inverts` (*2)
let inverts f g = f >> g <=> idCan be tested as:
[<Property>]
let ``Inverts Property`` i =
inverts (fun x -> x - 2) ((+) 2) iCommutative
Two functions can be executed in different orders and still produce the same result.
/// Checks whether two functions are commutative (endomorphism in relation to a unary operator).
/// a * b = b * a
/// quickCheck $ commutative (+)
let commutative f g = (f >> g) <=> (g >> f)Can be tested as:
[<Property>]
let ``Take Map Commutative Property`` xs =
xs <> [] ==> lazy
commutative (List.take 1) (List.map ((+) 1)) xs