Property-Based Testing with FsCheck

Prova integrates seamlessly with FsCheck to enable robust Property-Based Testing (PBT). Instead of writing static test cases, you can define properties that should hold true for a wide range of automatically generated inputs.

Installation

Add the Prova.FsCheck package to your test project:

dotnet add package Prova.FsCheck

Creating Property Tests

Decorate your test methods with the [Property] attribute instead of [Test] or [Fact]. Prova will detect the parameters and use FsCheck to generate random inputs.

using Prova.FsCheck;
using System.Linq;

public class MathTests
{
    [Property]
    public void AdditionIsCommutative(int a, int b)
    {
        if (a + b != b + a)
            throw new Exception("Commutativity broken!");
    }

    [Property]
    public void ReversingListTwiceYieldsOriginal(List<int> list)
    {
        var reversed = Enumerable.Reverse(list).ToList();
        var doubleReversed = Enumerable.Reverse(reversed).ToList();
        
        if (!list.SequenceEqual(doubleReversed))
             throw new Exception("Double reverse failed");
    }
}

Configuration

You can configure FsCheck runner parameters directly on the attribute:

[Property(MaxTest = 1000, MaxFail = 100)]
public void ExtensiveTest(int a) { ... }

Supported parameters:

• MaxTest: The maximum number of tests to run (default: 100).
• MaxFail: The maximum number of tests where inputs are discarded (default: 1000).
• StartSize: The size of the first test (default: 1).
• EndSize: The size of the last test (default: 100).
• Verbose: Set to true to output every generated input (useful for debugging).
• QuietOnSuccess: Suppress output on success.

Failure Reporting

When a property fails, Prova captures the precise input that caused the failure (and shrinking information) and reports it as a test failure.

Failed: MathTests.AdditionIsCommutative
Exception: Falsifiable, after 1 tests (0 shrinks) :
(1, 2)

Async Properties

Prova supports async property methods. Note that FsCheck drives the execution loop, so Prova handles the sync-over-async adaption automatically for property tests.

[Property]
public async Task AsyncOperationHolds(int value)
{
    await Service.ProcessAsync(value);
}