1 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Model-based Testing of a Software Bus applied on Core Flight Executive Dharmalingam Ganesan, Mikael Lindvall Dave McComas (NASA GSFC)

2 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Traditional Test Automation  Only test execution is automated  E.g. Junit, CuTest, etc.  Test cases are manually constructed  Effort intensive  Some issues with traditional testing:  Insufficient coverage of off-nominal behaviors  Tests are too-detailed with low-level details  Not easy to test multi-tasking architecture  More on this later.

3 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Model-based Testing (MBT)  The tester develops a model (a.k.a. testing models)  instead of writing suite of test cases  The model becomes the test oracle  Test cases are auto-generated from the model  based on requirements, API documentations  Key benefits:  Tester works at a high-level of abstraction  Innumerable number of test cases derived from the model  Triggers many, if not all, off-nominal behaviors  Precise specification

4 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering System under test (SUT) The Core Flight Software System (CFS) a mission-independent, platform-independent, Flight Software (FSW) environment integrating a reusable core flight executive (cFE) The CFS is a product-line developed by the NASA Goddard Space Flight Center (GSFC) CFS is implemented in C cFE layer of the CFS is open source

5 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering cFE/CFS Context Diagram Inter-task Message Router (SW Bus) Transponders Commands Real-time Telemetry (UDP) Comm Cards File downlink (CFDP) Summit Chip Mass Storage System CFDP File Transfer File Manager Local Storage Data Storage Event Services Executive Services Time Services 1553 Bus Support Software Bus Command Ingest Telemetry Output Table Services EDAC Memory Scrubber Self Test Memory Dwell Instrument Manager Checksum Memory Manager GN&C Applications (4) Mission Apps cFE core App CFS Applications Stored Commanding Software Scheduler Health & Safety Manager House- keeping Limit Checker

6 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering MBT of Software Bus  cFE has a software bus (SB)  Apps communicate indirectly using the SB  Publish-Subscribe architectural style  SB has unit-tests (developed by NASA GSFC)  Good coverage but  not taking multi-tasking into consideration  Goals: find defects related to multi-tasking (difficult!)  Generate test cases for SB  Generate the “bubbles” (the apps on previous slide)  Demonstrate the applicability of MBT  Developed an approach of testing SB  Allows testing of multi-tasking architectures

7 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Scope of the current model  Modeled the following behaviors  Create Pipes (to hold messages)  Delete Pipes  Subscribe to Messages  Send Messages  Receive Messages  Multiple Apps (dynamically instantiated)  Innumerable test cases (in C) auto-generated  Model based on Microsoft’s Spec Explorer Tool  Will get back to this

8 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Challenges of testing a SB  To test a SB we need apps that publish-subscribe  Apps are runtime tasks that communicate using the SB  Apps publish/subscribe to messages  Each app cannot decide on its own the correctness  Correctness depends on the global state of the system  E.g: subscribe(msg), RecvMsg() may not work if no other task is publishing any message  The order of execution of tasks also matters  Need a test architecture!

9 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Test Architecture – Key Ideas  Parent/Child architecture for testing  Each test case is a parent  Each test case runs as an app  At run-time, one or more child tasks are spanned by the parent  Model controls the behavior of the parent  All test assertions are decided by the parent  All child tasks share the codebase  How the parent and children communicate?  Why not just use the software bus itself?

10 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Test Architecture CFE Parent Result Pipe Child 1 Child 2 Child n Command Pipe All child tasks share the codebase

11 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Test Architecture – Key Ideas  Each child task subscribes to all commands, such as Create Pipe, Delete Pipe, Subscribe, etc.  Parent broadcast commands to all child tasks  Communication uses CFE infrastructure  Task id of the child is also part of the message struct  Only the target child can perform a certain command  Child tasks perform the command and send the return code back to the parent  Child tasks send out a result msg  Parent task subscribes to the result msg  The parent verifies test assertion  Asserts are generated from the model

12 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Spec Explorer – Brief Background  Tester develops a model (a.k.a. model program)  Spec Explorer runs as a plug-in to MS Visual Studio  Model programs are written in C# like syntax  The model program is a simplified version of the SUT  Spec Explorer generates state machines from models  Also checks whether model satisfies invariants  Helps in validating the model  Test cases are automatically derived from state machines  SUT’s behavior is automatically compared with model  Tests failure: Deviation between model and SUT  Tests success: model and SUT are consistent

13 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Abstractions for the model program  Model program is another implementation of the SUT  But we do not want to create two implementations  No one wants to maintain two implementations  No one wants to develop a system two times  How did we create a simplified version of the SUT?  Key idea: Apply abstractions Model of GPM, which uses CFE

14 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Sample abstractions for a model  Model is agnostic to multi-tasking complexity of the SB  Model has a very simple message structure  Message is modeled as an int (not C structures)  Message queues/pipes are also abstracted  Finite depth  Message queues are modeled as simple sequences  instead of using shared memory  No pointers, threads, semaphores at the model level  Very simple data structure using very basic data types  int, boolean, maps

15 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Structure of the model program E.g.: Number of apps, pipes Represent the state of the bus Used for excluding the uninteresting states Which states are good for terminating tests Models the actual logic of the software bus Preconditions for enabling the rule methods to fire Generates values for rule methods Utilties for rule methods and guards

16 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering State Data

17 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Fragments of the model program Rules are enabled only if Condition.IsTrue returns true

18 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Fragments of the guards

19 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Slicing the model for specific tests

20 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Generated from the model program We generate the model! In “regular” MBT you have to manually create the model.

21 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Generated test sequences - sample Each chain is a test case

22 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering SUT Adapter  Adapter wraps the SUT  Converts data/commands from the model into SUT’s syntax  Adapter simplifies modeling complexity  Methods of the model should map to the adapter  Our adapter is in C#  We “print” test code from our adapter in C  Converts C# tests into C tests  Recall that CFE’s SB interface is in C

23 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Our abstracted interface for Testing int32 InitApp_w(int32 appName); int32 CreatePipe_w(int32 appName, int32 pipeName, int32 pipeDepth); int32 DeletePipe_w(int32 appName, int32 pipeName); int32 Subscribe_w(int32 appName, int32 msgId, int32 pipeName); int32 UnSubscribe_w(int32 appName, int32 msgId, int32 pipeName); int32 RcvMsg_w(int32 appName, int32 pipeName, int32* actualMsgId); int32 SendMsg_w(int32 appName, int32 msgId);

24 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Sample generated test case void Parent_TestAppMain( void ) { int32 status; uint32 RunStatus = CFE_ES_APP_RUN; Parent_TestAppInit(); status = InitApp_w(APP_0); assert(status == CFE_SUCCESS); status = CreatePipe_w(APP_0, PIPE_0, 1); assert(status == CFE_SUCCESS); status = Subscribe_w(APP_0, MSG_0, PIPE_0); assert(status == CFE_SUCCESS); status = Subscribe_w(APP_0, MSG_1, PIPE_0); assert(status == CFE_SUCCESS); status = UnSubscribe_w(APP_0, MSG_1, PIPE_0); assert(status == CFE_SUCCESS); CFE_ES_ExitApp(RunStatus); }

25 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Advantages of using Model-Based Testing  The model focuses on the domain (easier to understand)  Instead of being source code oriented (harder to understand)  We automatically generate an endless number of executable test cases (high coverage)  Instead of manually writing individual test cases  The information is in one place: in the model, easy to maintain  Instead of being spread out (hard to maintain)  The test cases can easily be run over and over again

26 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Advantages of using Spec Explorer  Generated tests are pretty readable  This is due to the ability to slice models into smaller models  Data parameters are well handled  E.g., Model can be configured to test multiple apps  Models are programs  Ideal for programmers (who prefer coding)  Models can be formally verified  Invariants encoded in the model help to validate the model

27 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Challenges with Spec Explorer  Modeling errors can lead to infinite state machine  Need to be careful even for small models (e.g., int parameters)  Syntax for slicing the model is powerful but not that easy  Easy to misuse some of (algebraic) operators for slicing  Completeness of our slices  Did we miss any combination of behaviors during slicing?  Model debugging. For example:  Why a new state was generated?  Where/Why the invariants are violated?

28 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Applicability to other flight software  The same approach is applicable to other types of sw  Requirements are that  The software has an interface (e.g. API, GUI)  Through which commands (stimuli) can be sent  Through which results (responses) can be received  Need (some) specification  Optional: Sample test cases, API usage examples

29 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Conclusion  MBT works well for testing of multi-tasking architecture  In this case of a software bus  Parent/Child test architecture facilitates testing  Individual tasks cannot decide correctness of their own  Parent coordinates with children and asserts correctness  Models and generated state machines: a good spec!  Innumerable number of test cases from the model  Test cases are agnostic to cFE syntax but still executable  Need to be careful in managing the model’s complexity  Abstraction is important  Otherwise the model will be as complex as the system under test

30 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Acknowledgement  Jan-Philip Quirmbach (Fraunhofer Intern)  cFE is open source – not an issue for foreign interns  Alan Cudmore (NASA GSFC)  OSMA SARP:  Martha Wetherholt (NASA HQ)  Ken Rehm (NASA IV&V)  Ricky A. Forquer (NASA IV&V)  This work was partly funded by SARP

31 © 2014 Fraunhofer USA, Inc. Center for Experimental Software Engineering Questions  Dharma Ganesan