How do I test "should not contain" using FsUnit.Xunit?

Question

I am trying to test that a collection does not contain a value using FsUnit.Xunit.

open FsUnit.Xunit

[<Fact>]
let ``simple test`` () =
  let xs = [ 1; 2; 3 ]

  xs |> should contain 1

  xs |> should not contain 99 // Not real code

I have also tried using not'.

How should I write this?

Answer 1

You just need to wrap it in parenthesis since it expects a constraint (and not a function). contain is a function that expects a value and returns a constraint.

 xs |> should not' (contain 99)