anchor.diff:          ; EveryShrink = everyShrink
           ; Size= size
           ; Runner = runner
  +        ; Replay = None
           }
   
   [<AbstractClass>]
  
positive.code:     member x.EveryShrink with get() = everyShrink and set(v:Func<obj array,string>) = everyShrink <- fun os -> v.Invoke(List.to_array os)
      member x.Size with get() = size and set(v:Func<double,double>) = size <- v.Invoke
      member x.Runner with get() = runner and set(v) = runner <- v
      member internal x.ToConfig() =
          { MaxTest = maxTest
          ; MaxFail = maxFail 
  
negative.code:     let mutable everyShrink = Runner.quick.EveryShrink
      let mutable size = Runner.quick.Size
      let mutable runner = Runner.quick.Runner
      let mutable replay = Runner.quick.Replay
      member x.MaxNbOfTest with get() = maxTest and set(v) = maxTest <- v
      member x.MaxNbOfFailedTests with get() = maxFail and set(v) = maxFail <- v
      member x.Name with get() = name and set(v) = name <- v
  