anchor.diff:  
   [<TestCase>]
   let map () : unit =
  -    [(5, "a"); (3, "b")]
  -    |> IntMap.ofList
  -    |> IntMap.map (sprintf "%i:%s")
  -    |> should equal (
  -        IntMap.ofList [(5, "5:a"); (3, "3:b")])
  +    [| (5, 'a'); (3, 'b'); (11, 'f'); (2, 'd');
  +        (17, 'a'); (4, 'g'); (12, 'b'); (14, 'c'); |]
  +    |> IntMap.ofArray
  +    |> IntMap.map (sprintf "%i:%c")
  +    |> should equal (IntMap.ofArray
  +        [| (5, "5:a"); (3, "3:b"); (11, "11:f"); (2, "2:d");
  +            (17, "17:a"); (4, "4:g"); (12, "12:b"); (14, "14:c"); |])
   
   //[<TestCase>]
   //let filter () : unit =
  
positive.code: 
  [<TestCase>]
  let containsKey () : unit =
      [| (5, 'a'); (3, 'b'); (11, 'f'); (2, 'd');
          (17, 'a'); (4, 'g'); (12, 'b'); (14, 'c'); |]
      |> IntMap.ofArray
  
negative.code: 
  [<TestCase>]
  let union () : unit =
      let x = IntMap.ofArray [| (4, 'g'); (5, 'a'); (11, 'f'); (14, 'c'); (17, 'a'); |]
      let y = IntMap.ofArray [| (2, 'd'); (3, 'b'); (4, 'G'); (11, 'F'); (12, 'b'); |]
      let z = IntMap.ofArray [| (2, 'd'); (3, 'b'); (4, 'G'); (5, 'a'); (11, 'F'); (12, 'b'); (14, 'c'); (17, 'a'); |]
      let result_xy = IntMap.union x y
      let result_yx = IntMap.union y x
  
      let qq =
          x
          |> IntMap.add 2 'd'
          |> IntMap.add 3 'b'
          |> IntMap.add 4 'G'
          |> IntMap.add 11 'F'
          |> IntMap.add 12 'b'
  
  
  //    let x = IntMap.ofArray [| (5, 'a'); (11, 'f'); (17, 'a'); (4, 'g'); (14, 'c'); |]
  //    let y = IntMap.ofArray [| (3, 'b'); (11, 'F'); (2, 'd'); (4, 'G'); (12, 'b'); |]
  //    let z = IntMap.union y x
  //    let w = IntMap.ofArray [| (5, 'a'); (3, 'b'); (11, 'F'); (2, 'd'); (17, 'a'); (4, 'G'); (12, 'b'); (14, 'c'); |]
  
      IntMap.union
          (IntMap.ofArray [| (3, 'b'); (11, 'F'); (2, 'd'); (4, 'G'); (12, 'b'); |])
          (IntMap.ofArray [| (5, 'a'); (11, 'f'); (17, 'a'); (4, 'g'); (14, 'c'); |])
      |> should equal (
          IntMap.ofArray [| (5, 'a'); (3, 'b'); (11, 'F'); (2, 'd'); (17, 'a'); (4, 'G'); (12, 'b'); (14, 'c'); |])
  
  [<TestCase>]
  let ofSeq () : unit =
  