1. Automated Model-Based Testing of Hybrid Systems Michiel van Osch PROSE January 25, 2007 13

2. 2 Motivation Hybrid Systems Testing might be expensive, dangerous, or resources might be limited Discrete and real-time model-based testing does not test the continuous aspects of the system

3. 3 Content Part I: Theory –Model-based Testing –Input-Output Conformance & Discrete Tests –Hybrid Systems –Hybrid Input-output Conformance –Hybrid Tests –Results Part II:Tool –Test Architecture –Specification –Tester –The Connection with the Implementation Under Test –Adapter –Limitations and Future Work –Case Study: Vacuum Control

4. 4 Model-Based Testing model SUT IUT conforms to model pass fail test tool test generation tool test execution tool IUT passes tests IUT conf model    soundexhaustive

5. 5 Input-output Conformance for Discrete Systems Impl. ioco Spec. iff for all traces α: out(Impl. after α)  out(Spec. after α) If there is an output action from state s then out(s) = {o in O| s →} else out(s) = {δ} Furthermore, out(S) = U s  S out(s)

6. 6 Test-case Generation and Execution 1.Terminate with verdict pass 2.Select an input from the specification and apply it to the implementation 3.Observe an output or a timeout from the implementation and check if it is allowed according to the specification

7. 7 Example s1s0 s2 s3 ?Activate ?Button2 ?Button1 !XLCoffee !Coffee t0 t1 ?Activate t3 ?Button2 t2 ! δ Fail !Coffee!XLCoffee Pass !XLCoffee Fail !Coffee ! δ

8. 8 Hybrid Systems In Practice: –Discrete behavior plus continuous behavior –Continuous behavior can be input observed through sensors or output generated by actuators In Theory: –Discrete actions plus flow of continuous variables (trajectories) –Variables can be input variables and output variables –Hybrid Transition Systems

9. 9 Hybrid Systems (Output Only) Time Coffee 0 ?Button1 ?Button2 s1s0 s2 s3 ?Activate ?Button2 ?Button1 Coffee’ = 4 cl/sec. Δt = 8 sec. Coffee’ = 3 cl/sec. Δt = 5 sec. Coffee’ = 0 Δt = 1 sec. Coffee’ = 0 Δt = 1 sec..

10. 10 Hybrid Systems (Including Input) Water s1s0 s2 s3 ?Activate ?Button2 ?Button1 Water’ = 4 cl/sec. Coffee’ = Water’ Δt = 8 sec. Water’ = 3 cl/sec. Coffee’ = Water’ Δt = 5 sec. Water’ = 0 Coffee’ = 0 Δt = 1 sec. Water’ = 0 Coffee’ = 0 Δt = 1 sec..

11. 11 Hybrid Conformance For every reachable state, the set of output actions possible by the implementation is a subset of the set of output actions possible by the specification For every reachable state, the set of trajectories possible by the implementation is a subset of the set of trajectories possible by the specification In contrast to ioco, no quiescence action because there is always continuous output.

12. 12 Continuous Output Only Impl. is input-output conform a Spec. iff for all traces α: out(Impl. after α)  out(Spec. after α) and traj(Impl. after α)  traj(Spec. after α) s1s0 s2 s3 ?Activate ?Button2 ?Button1 Coffee’ = 4 cl/sec. Δt = 8 sec. Coffee’ = 3 cl/sec. Δt = 5 sec. Coffee’ = 0 Δt = 1 sec. Coffee’ = 0 Δt = 1 sec..

13. 13 With Continuous Input The implementation is input enabled (for both discrete behavior and continuous behavior). We do not require the specification to be input complete. Impl. is input-output conform a Spec. iff for all traces α: out(Impl. after α)  out(Spec. after α) and traj(Impl. after α)  traj(Spec. after α) Does not work!! Solution: Look at the trajectories of the Implementation with respect to the trajectories of input variables of the Specification

14. 14 Hybrid Conformance (Continuous Input plus Output) infilter(traj(Impl. after α), traj(Spec. after α))  traj(Spec. after α) s1 s3 ?Button2 Water’ = 0 Coffee’ = 0 Δt = 1 sec.. s4 Water’ = 0 Coffee’ = 0 Δt = 3 sec.. s5 !Out of Cups Water’ = 0 Coffee’ = 0 Δt = 1 sec.. u1 u3 ?Button2 Water’ = 0 Coffee’ = 0 Δt = 1 sec.. u4 Water’ = 0 Coffee’ = 0 Δt = 3 sec.. u5 !Out of Cups Water’ = 0 Coffee’ = 0 Δt = 1 sec.. Specification Implementation Water’ = 0 Coffee’ = 0 Δt = 1 sec.. Still does not work because …

15. 15 Hybrid Conformance (continuous input plus output) If there is a trajectory from state s then out(s) = {o in O| s →}  {ξ} else out(s) = {o in O| s →} Impl. hioco Spec. iff for all traces α: out(Impl. after α)  out(Spec. after α) and infilter(traj(Impl. after α), traj(Spec. after α))  traj(Spec. after α)

16. 16 Hybrid Tests A Special kind of Hybrid Transition Systems: Tree like structure Two terminal states: pass and fail Deterministic for actions Strongly time deterministic for trajectories

17. 17 Hybrid Tests 1.Terminate with verdict pass 2.Select an input from the specification and apply it to the implementation s1s0 ?Activate Water’ = 0 Coffee’ = 0 Specification t0 t1 ?Activate Test

18. 18 Hybrid Test-case Generation 3.If an output action has to happen immediately according to the specification then observe an output action and check if it is allowed according to the specification or let time pass by selecting and applying and observing a trajectory Fail s4s5 !”Out of Cups” Coffee’ = 0 Water’ = 0 Δt = 1 Specification t4 Pass !”Out of Cups” Test-Case Coffee’ = 0 Water’ = 0 Δt = 1

19. 19 Hybrid Test-case Generation 4.Select an input trajectory from the specification, apply it to the implementation and observe the output trajectory simultaneous, possibly interrupted by an output action. Specification s1 Water’ = 0 Coffee’ = 0 Δt = 1 Test t1 t2 Water’ = 0 Coffee’ = 0 Δt = 1 Fail !”out of cups” Water’ = 0 Coffee’ = 3 Δt = 1

20. 20 Results A hybrid conformance theory Proven Sound and exhaustive A Natural extension of discrete and timed conformance theories

21. 21 Content Part I: Theory –Model-based Testing –Input-Output Conformance & Discrete Tests –Hybrid Systems –Hybrid Input-output Conformance –Hybrid Tests –Results Part II: Tool –Test Architecture –Specification –Tester –The Connection with the Implementation Under Test –Adapter –Limitations and Future Work –Case Study: Vacuum Control

22. 22 Libraries Tester Architecture Specification: The Model from which Tests are Generated Tester: Implements The Test Algorithm and Gives the Verdict Adapter: Translated Input/Output from Model to a format suitable for the Implementation Under Test and vice versa Medium: The Interface between Tester and Implementation IUT: The Implementation Under Test Spec Tester Adapter Medium IUT

23. 23 Libraries Specification Needs to: Model Discrete behavior and Continuous Behavior Make Distinction between Input Actions, Output Actions, and Internal Actions Make Distinction between Input Variables, Output Variables and Internal Variables Model in an Intuitive way Medium Adapter Spec Tester IUT

24. 24 Libraries Specification Medium Adapter Spec Tester proc Control(cont V: real, chan h,out: real)= |[ *(V h!!1.0; out!!1.0 ; V >= 10 -> h!!0.0; out!!0.0) ]| proc Env(cont V: real, chan h: real)= |[ var n: real = 0.0 :: V’=3.0*n - 1.0 | *(h?n) ]| model Spec()= |[ cont V: real = 10.0, chan h,out: real :: Control(V,h,out)|| Env(V, h) ]| IUT

25. 25 Libraries Tester Implements: On the Fly Test Generation –Select Input from Specification –Apply Input –Observe Output –Compare the Observed Output with the Output allowed by the Specification –Give a Verdict or Continue Test Medium Adapter Spec Tester IUT

26. 26 On the Fly Testing proc ControlS(cont V: real, chan h: real)= |[ var n: real = 0.0 :: V’=3.0*n - 1.0 | *(V n:=1.0; h!!1.0 ; V >= 10 -> n:=0.0; h!!0.0) ]| model Spec()= |[ cont V: real = 10.0, chan h: real :: ControlS(V,h) ]| V=10 V=2 V’=3.0*0.0-1.0 Δt = 8 sec. Select Input ( χ )(Manually/ Automatic) V=2 h!!1.0 pass fail h!!0.0 Compare Values ( χ, Maple) Pass Give Verdict (with trace) Continue Apply (Via adapter) Pressure’= -1.0 mbar/sec Δt = 8 sec. IUT Pump OFF Observe (Via adapter) IUT

27. 27 Additional Libraries χ –stepper for computing sets of allowed transitions and current state of the specification E.g. Maple for comparing observed continuous output (samples) with specified trajectories and comparing observed discrete output values with specified send actions Libraries Medium Adapter Spec Tester IUT

28. 28 Libraries The Connection Medium Jabber χ Model TCP/IP Labview Controller WiresElectronics Buttons/ Sensors Robot Arm Adapter Spec Tester IUT

29. 29 Libraries Tester The Adapter Implements –Mapping of Variables/Actions of Specification to a Implementation and vice versa (e.g. channels to function calls, or variables to wires) –Translating Input/Output of Specification to Implementation and vice versa (e.g. functions to samples, or signals) Medium Adapter Spec IUT

30. 30 Limitations and Future Work This is just a prototype, there are shortcomings! –Real Time Testing is Not Possible Yet –The complexity of Continuous behavior is limited by the Hybrid χ –stepper implementation. E.g. currently only standard differential equations. –Models are not ‘ideal’ for testing. E.g. in case of identifying input and output –For performance reasons we only deal with deterministic specifications. –We assume that the communication medium is reliable Adaptation of theory for Sampling and Inaccuracy Case Studies

31. 31 Real Time Generating and applying input (e.g. samples) Observing output and Time at which output Occurred in the Implementation

32. 32 Limitations and Future Work This is just a prototype, there are shortcomings! –Real Time Testing is Not Possible Yet –The complexity of Continuous behavior is limited by the Hybrid χ –stepper implementation. –Models are not ‘ideal’ for testing. –For performance reasons we only deal with deterministic specifications. –We assume that the communication medium is reliable Adaptation of theory for Sampling and Inaccuracy Case Studies

33. 33 The Vacuum Case Lithography Process takes place in vacuum Waferstepper has Five Chambers Chambers are kept in Vacuum by a system of Pumps and Valves Pumps and Valves are Controlled by Software (discrete) Software observes Pressure in Chambers through Sensors (continuous)

34. 34 Activities Modeling Hardware in Hybrid χ and Stand Alone Simulation Modeling (translating) Hardware in discrete (timed) χ and Integration with Software Controller Modeling (translating) in Uppaal for Model Checking Testing Models and Software Controller with the Hybrid Tester

35. 35 Questions?