FsUnit is a library for use with the F# programming language. It is a set of extensions that add a special testing syntax (see below) to your favorite unit-testing framework so that you don't have to learn a new testing framework but you also get to take advantage of everyone's favorite new language.

Syntax

With FsUnit, you can write unit tests like this:

• One object equals or does not equal another:

1 |> should equal 1

1 |> should not (equal 2)

• A List, Seq, or Array instance contains or does not contain a value:

[1] |> should contain 1

[] |> should not (contain 1)

• A List or Array instance has a certain length:

anArray |> should haveLength 4

• A Collection instance has a certain count:

aCollection |> should haveCount 4

• A function should throw a certain type of exception:

(fun () -> failwith "BOOM!" |> ignore) |> should throw typeof<System.Exception>

• A number of assertions can be created using the be keyword:

true |> should be True

false |> should not (be True)

[] |> should be Empty

[1] |> should not (be Empty)

"" |> should be EmptyString

"" |> should be NullOrEmptyString

null |> should be NullOrEmptyString

null |> should be Null

anObj |> should not (be Null)

anObj |> should be (sameAs anObj)

anObj |> should not (be sameAs otherObj)

FULL EXAMPLE

Here is a complete set of tests from the FsUnit.NUnit examples:

#r "FsUnit.NUnit.dll"
#r "nunit.framework.dll"
open NUnit.Framework
open FsUnit

type LightBulb(state) =
    member x.On = state
    override x.ToString() =
        match x.On with
        | true  -> "On"
        | false -> "Off"

[<TestFixture>] 
type ``Given a LightBulb that has had its state set to true`` ()=
    let lightBulb = new LightBulb(true)

    [<Test>] member test.
     ``when I ask whether it is On it answers true.`` ()=
            lightBulb.On |> should be True

    [<Test>] member test.
     ``when I convert it to a string it becomes "On".`` ()=
            string lightBulb |> should equal "On"

[<TestFixture>]
type ``Given a LightBulb that has had its state set to false`` ()=
    let lightBulb = new LightBulb(false)
    
    [<Test>] member test.
     ``when I ask whether it is On it answers false.`` ()=
            lightBulb.On |> should be False
    
    [<Test>] member test.
     ``when I convert it to a string it becomes "Off".`` ()=
            string lightBulb |> should equal "Off"