anchor.diff:      schemaUpdated
   
     override this.TestResults =
  -    testResults :> IObservable<_>
  +    testResults
   
     override this.Start() =
       start ()
  
positive.code:     cancel ()
      match OneshotTestAssembly.ofFile file with
      | Success testAssembly ->
        let subscriptions = new CompositeDisposable()
        let unload () =
          subscriptions.Dispose()
          cancel()
        currentTestSchema.Value <- testAssembly.Schema
        testAssembly.TestResults.Subscribe
          ( testResults.OnNext
          , ignore >> unload
          , unload
          )
        |> subscriptions.Add
        currentTestAssembly.Value <- Some testAssembly
        testAssembly.Start()
      | Failure e ->
  
negative.code:       )
  
    let testResults =
      currentTestAssembly
        .Select
          (fun testAssembly ->
            match testAssembly with
            | Some testAssembly ->
              testAssembly.TestResults
              |> fun o -> o.Finally(fun () -> cancel ())
            | None ->
              Observable.Empty()
          )
      |> fun o -> o.Switch()
  
    let subscription =
      new SingleAssignmentDisposable()
  