anchor.diff:  open NUnit.Framework
   open StackVM
   
  -module InstructionTests =
  +module Instructions =
   
       [<Test>]
       let ``Push 4 pushes 4 on the stack`` () =
  
positive.code:         let result = 
              [Push 4; Print]
              |> Stack.fold Stack.initialState
          Assert.AreEqual(List.head result, 4)
negative.code:     [<Test>]
      let ``Multiply multiplies`` () =
          let result = 
              [Push 4; Push 2; Multiply]
              |> Stack.fold Stack.initialState
          Assert.AreEqual(List.head result, 8)    
  
  