FsUnit is a stand-alone specification framework for use with the F# programming language. Written itself in F#, it offers a functional alternative to traditional imperative frameworks.

Specification Syntax

With FsUnit, you can write specifications like this:

• One object equals or does not equal another:

1 |> should equal 1

1 |> should not' (equal 2)

• A collection type contains or does not contain a value:

["item"] |> should contain "item"

["item"] |> should not' (contain "not item")

• A collection type has a certain number of items:

personList |> should have 4 "people"

• A function should throw a certain type of exception:

(fun () -> failwith "BOOM!") |> should (raise'<FailureException>)

• Boolean, Null, NullOrEmpty, Empty, and SameAs assertions have their own helpers:

true |> should be True

false |> should not' (be True)

"" |> should be Empty

"a string" |> should not' (be Empty)

"" |> should be NullOrEmpty

null |> should be NullOrEmpty

null |> should be Null

anObj |> should not' (be Null)

anObj |> should be (SameAs(otherObj))

The specs and spec Keywords

Let FsUnit manage the storage and execution of your specs, use the specs keyword:

specs "My Specs" [
    spec "A number should equal itself."
        (1 |> should equal 1)
]

printfn "%s" (Results.summary())

For more examples of using the spec and specs keywords, see the examples.

FULL EXAMPLE

The full code for a specification in FsUnit looks like this:

#light
#r "FsUnit.dll"
open FsUnit

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

let onSpecs =   
    let lb = LightBulb(true)
    
    specs "On Specs" [
        spec "On should be true."
            (lb.On |> should be True)
        spec "String representation should equal \"On\"."
            (lb.ToString() |> should equal "On")
    ]

let offSpecs =
    let lb = LightBulb(false)
    
    specs "Off Specs" [
        spec "Off should be false."
            (lb.On |> should be False)
        spec "String representation should equal \"Off\"."
            (lb.ToString() |> should equal "Off")
    ]

printfn "%s" (Results.summary())