nw-pbt-dotnet

PBT .NET -- FsCheck + CsCheck (C#/F#)

Framework Selection

Framework	Language	Shrinking	Stateful	Parallel	Choose When
FsCheck	C#/F#	Type-based	No	No	F#-first projects, or C# needing mature PBT
CsCheck	C#	PCG-based	Yes	Yes (linearizability)	C# projects needing concurrent testing
fsharp-hedgehog	F#	Integrated	No	No	F# projects wanting modern integrated shrinking

C# default: CsCheck (better shrinking, stateful + parallel). F# default: FsCheck or fsharp-hedgehog.

Quick Start (FsCheck)

// C#
using FsCheck; using FsCheck.Xunit;

public class SortProperties
{
    [Property]
    public bool SortPreservesLength(List<int> xs) =>
        xs.OrderBy(x => x).Count() == xs.Count;
}

// F#
open FsCheck

let propSortIdempotent (xs: int list) =
    List.sort (List.sort xs) = List.sort xs

Check.Quick propSortIdempotent

Generator Cheat Sheet (FsCheck)

C#

Arb.Generate<int>()                    // any int
Gen.Choose(0, 100)                     // bounded
Arb.Generate<string>()
Arb.Generate<List<int>>()

// Custom generator
public static Arbitrary<Email> EmailArb() =>
    Arb.From(
        from name in Arb.Generate<NonEmptyString>()
        select new Email($"{name}@example.com")
    );

Arb.Register<MyGenerators>();          // register custom arbitraries

F#

Gen.choose (0, 100)
Gen.elements [1; 2; 3]
Gen.oneof [gen1; gen2]
Gen.frequency [(80, gen1); (20, gen2)]
Gen.listOf (Gen.choose (0, 100))

Gen.choose (0, 100) |> Gen.map (fun x -> x * 2)

gen {
    let! xs = Gen.listOf (Gen.choose (0, 100))
    let! x = Gen.elements xs
    return (xs, x)
}

Quick Start (CsCheck)

using CsCheck;

[Fact]
public void Sort_Preserves_Length()
{
    Gen.Int.Array
       .Sample(arr => arr.OrderBy(x => x).Count() == arr.Length);
}

CsCheck Generators

Gen.Int                                // any int
Gen.Int[0, 100]                        // bounded
Gen.Double
Gen.String
Gen.Bool
Gen.Int.Array                          // int[]
Gen.Int.List                           // List<int>
Gen.Int.HashSet                        // HashSet<int>
Gen.Int.Select(x => x * 2)            // map
Gen.Select(Gen.String, Gen.Int, (name, age) => new User(name, age))
Gen.OneOf(Gen.Int.Select(x => (object)x), Gen.String.Select(x => (object)x))
Gen.Int.Where(x => x > 0)             // filter