Property based testing - Updating FsCheck to version 3.x

f you have never heard about Property based testing, I would recommend to check my blog series about it first. But if you are too lazy to go through all these posts, here is a short definition:

Property-based testing is a powerful testing methodology used in software development to verify that a system behaves correctly across a wide range of inputs. Instead of writing individual test cases with specific inputs and expected outputs, property-based testing defines properties—general rules that should always hold true for a given system.

It serves as an alternative to example based testing where we focus on a set of example cases to validate the behavior of our code.

There are a lot of libraries out there that help you write Property Based Tests. In .NET I mainly use FSCheck and CSCheck. As I’m doing more and more Python, I also start using Property Based Tests there through Hypothesis.

In this post I’ll focus on FSCheck and how to update to the latest version as some breaking changes were introduced and the documentation is not that helpful when upgrading (although you can find some details in the release notes).

Updating FsCheck to version 3.x

FsCheck works for both C# and F#. Due to the language differences however the 2.x version didn’t feel always that intuitive when using it in C#. To improve the experience in version 3.x, the API is now split into a functional (for F# consumers) and fluent (for C# and VB.NET consumers) interface.

Update to the latest version of FsCheck:

dotnet add package FsCheck

dotnet add package FsCheck.XUnit

After upgrading I got a few compiler errors that I had to fix.

First add a reference to the FSCheck.Fluent namespace:

This already fixes a lot of the errors I got.

To make the Prop.Throw work again I had to add a reference to the FSCheck.FSharp namespace:

Next thing I had to do was to replace the calls to Arb.Default with ArbMap.Default:

A last change I had to make was to update the configuration code as the configuration object is now immutable:

More information

Property based testing in C#–Part 1

Property based testing in C#–Part 2

Property based testing in C#–Part 3

Property based testing in C#–Part 4

Property based testing in C#–Part 5

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