private String leave() {
    return "leave";
  }

  public final void testMutualExclusion() throws Exception {
    thread1.callAndAssertReturns(enter());
    thread2.callAndAssertBlocks(enter());
    thread1.callAndAssertReturns(leave());
    thread2.assertPriorCallReturns(enter());
  }

  public final void testTryEnter() throws Exception {
    thread1.callAndAssertReturns(true, tryEnter());

  private String leave() {
    return "leave";
  }

  public final void testMutualExclusion() throws Exception {
    thread1.callAndAssertReturns(enter());
    thread2.callAndAssertBlocks(enter());
    thread1.callAndAssertReturns(leave());
    thread2.assertPriorCallReturns(enter());
  }

  public final void testTryEnter() throws Exception {
    thread1.callAndAssertReturns(true, tryEnter());

        name == "first"
        tracker.root
        tracker.segments.empty
        tracker.toRelativePath() == ""
    }

    def "can enter and leave second level"() {
        given:
        tracker.enter("root")
        tracker.enter("first")
        when:
        tracker.enter("second")
        then:
        !tracker.root
        tracker.segments as List == ["first", "second"]

    }
  }
  attr {
    key: "value"
    value {
      tensor {
        dtype: DT_INT32
        tensor_shape {
        }
        int_val: 0
      }
    }
  }
}
node {
  name: "Enter"
  op: "Enter"
  input: "Const"
  attr {
    key: "T"
    value {
      type: DT_INT32
    }
  }
  attr {
    key: "frame_name"
    value {
      s: "while_context"
    }
  }
  attr {

    %Enter, %ctl_0 = Enter(%Const) [%arg.ctl] name("while/Enter") {T = i32, frame_name = "while/while_context", is_constant = false, parallel_iterations = 10 : i64} : (tensor<i32>) -> (tensor<*xi32>)
    %NextIteration, %ctl_1 = NextIteration(%Const) [%arg.ctl] name("while/NextIteration") {T = i32} : (tensor<i32>) -> (tensor<*xi32>)

  Scope root = Scope::NewRootScope().ExitOnError();

  Output a = ops::Const(root.WithOpName("a"), Input::Initializer(0.0));
  Output enter =
      ops::internal::Enter(root.WithOpName("enter"), a, "only_frame");
  Output exit = ops::internal::Exit(root.WithOpName("exit"), enter);
  Output b = ops::Add(root.WithOpName("b"), a, exit);

  FixupSourceAndSinkEdges(root.graph());

  GraphCycles cycles;

    %Enter, %ctl_0 = Enter(%Const) name("while/Enter") {T = i32, frame_name = "while/while_context", is_constant = false, parallel_iterations = 10 : i64} : (tensor<i32>) -> (tensor<*xi32>)
    %NextIteration, %ctl_1 = NextIteration(%Add) name("while/NextIteration") {T = i32} : (tensor<*xi32>) -> (tensor<*xi32>)

        tracker.leaveDynamicCall(entryPoint2)
        tracker.leaveDynamicCall(entryPoint1)

        then:
        log == ["enter", entryPoint1, "enter", entryPoint2, "leave", entryPoint2, "leave", entryPoint1]
    }

    def "throws exception on mismatched calls"() {
        when:
        tracker.enterDynamicCall(new Object())
        tracker.leaveDynamicCall(new Object())

        then:

Enter username:
Enter password:
Welcome, secret-user!

            def a = it.askQuestion("enter value", "value")
            def b = it.askQuestion("enter another value", "value")
            [a, b]
        }

        then:
        1 * outputEventBroadcaster.onOutput(_ as UserInputRequestEvent)
        1 * outputEventBroadcaster.onOutput(_) >> { TextQuestionPromptEvent event ->
            assert event.question == "enter value"
        }