anchor.diff:      xs.Count |> equal 1
           
   
  +[<Test>]
  +let ``Set.contains works``() =
  +    let xs = set [1]
  +    xs.Contains 1 |> equal true
  +    xs.Contains 2 |> equal false
  +
  +
  +[<Test>]
  +let ``Set.remove works when item is present``() =
  +    let xs = set [1] 
  +    xs.Remove 1 |> equal true
  +    xs.Count |> equal 0
  +
  +[<Test>]
  +let ``Set.remove works when item is not present``() =
  +    let xs = set [1; 2] 
  +    xs.Remove 3 |> equal false
  +    xs.Count |> equal 2
  +
  +[<Test>]
  +let ``Set.union works``() =
  +    let xs = set [1; 2] 
  +    let ys = set [2; 4]
  +    xs.UnionWith ys
  +    (xs.Contains 1 && xs.Contains 2 && xs.Contains 4)
  +    |> equal true
   
   [<Test>]
   let ``HashSet creation works``() =
  
positive.code:     let x2 = Newtonsoft.Json.JsonConvert.DeserializeObject<HashSet<R>> json
      #endif
      (0, x2) ||> Seq.fold (fun acc v -> acc + v.i) |> equal 3
  
negative.code: [<Test>]
  let ``HashSet.Add works``() =
      let hs = HashSet<_>()
      hs.Add("A", "Hello") |> equal true
      hs.Add("B", "World!") |> equal true
      hs.Count |> equal 2
  
  [<Test>]
  let ``HashSet.Clear works``() =
      let hs = HashSet<_>()
      hs.Add("A", 1) |> equal true
      hs.Add("B", 2) |> equal true
      hs.Clear()
      hs.Count |> equal 0
  
  [<Test>]
  let ``HashSet.Contains works``() =
      let hs = HashSet<_>()
      hs.Add("Hello") |> equal true
      hs.Add("World!") |> equal true
      hs.Contains("Hello") |> equal true
      hs.Contains("Everybody!") |> equal false
  
  