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FsCheck integrates with the xUnit.NET testing framework by adding a PropertyAtttribute. To use it, attribute your test method with Property instead of xUnit's built-in Fact, and you can now give your test arguments. These are randomly generated by FsCheck. You can also use all of the normal property combinators in the Prop namespace.


let ``abs(v) % k equals abs(v % k)`` v (NonZeroInt k) = 
    (abs v) % k = abs(v % k)

let ``divMod should satisfy definition`` (x:int) (y:int) = 
    y <> 0 ==> lazy (let (d,m) = divMod x y in d*y + m = x) 

Note that Property test methods, as opposed to Fact, don’t need to return unit – they can return anything that’s testable with FsCheck, including bool. But since a test fails in FsCheck when it throws an exception, you can still use the Assert class if you like.

You can also use FsUnit or Unquote or whatever to write your assertions. FsCheck does not care – it does the hard work of generating random values and shrinking them if the test fails and generally tries to get out of your way for the rest.

You can set various configuration parameters using the Property attribute, which then apply to that method only. Most of these are self-explanatory (e.g. the number of tests to run).

Finally, you can override the random generation for certain types on one test method only:

type TestArbitrary1 =
    static member PositiveDouble() =
        |> Arb.mapFilter abs (fun t -> t >= 0.0)

[<Property( Arbitrary=[| typeof<TestArbitrary1> |] )>]
let ``should register Arbitrary instances from Config in last to first order``(underTest:float) =
    underTest >= 0.0 

Here the generator for float is overridden to generate only positive floats.

Last edited Aug 13, 2012 at 2:20 PM by kurt2001, version 3


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