Getting Started with FSpec

This post will give a quick guide of how to get started with FSpec.

Generally, you would want to have unit tests separated from the production code
that is under test, so start by creating a new F# project.

The FSpec core contains code that can discover and execute the tests in an
assembly, so by far the easiest way to get started is to create a console


Once you have created the application, add the FSpec NuGet package.

PM> Install-Package FSpec
Installing 'fspec 0.0.7'.
Successfully installed 'fspec 0.0.7'.
Adding 'fspec 0.0.7' to MySpecs.
Successfully added 'fspec 0.0.7' to MySpecs.

Your console application should have a Program.fs file. Edit it, and place the
following code.

let main argv = 
    System.Reflection.Assembly.GetExecutingAssembly ()
    |> FSpec.TestDiscovery.runSingleAssembly

Set your start-up project to be your console application, and run your
application. You should see the following:


So let’s start by writing the first spec. Add a file, MyFirstSpec.fs

module MyFirstSpec
open FSpec.Dsl
open FSpec.Matchers

let specs =
  describe "my first spec" [
    it "should start with a failing test" <| fun _ ->
      false.Should be.True

Run the specs, and you should see the following output


The namespace FSpec.Core.Dsl contains the types necessary for building the
the tests.

The namespace FSpec.Core.MatchersV3 contains the assertion framework. The
types in this namespace will probably end up in FSpec.Core.Matchers, but at
the time of writing, this namespace contains a deprecated matcher framework.

When the framework gets to a more mature state, these modules will probably be
tagged with the AutoOpen attribute, so you only need to open FSpec.Core.
But not having AutoOpen on these modules does allow for alternative or
experimental variations to live in new modules, and thus not breaking existing

You can compile the specs to a .dll and use a dedicated test runner, but just
wrapping the specs in a self hosting executable is a lot easier to begin with.

When you want to run the specs, just run the your start-up project. If you need to
debug, just debug your start-up project.


Happy spec’ing.