System Testing

1. System Testing • Earlier we have stated the 2 views of testing: • To show that the software works(according to specification) • To detect as many defects(and have them fixed prior to releasing to the users) as possible • In system testing we are more interested in showing that the system, as a whole with all the “major” specifications – especially cross-component, is working. • Still Interested in knowing which“major” function is not working.(But this should be rare if we completed functional and component test properly.) • We are not focused on all types of exception during systems test, but want to make sure that when multiple paths (threads) are executed, it still works according to the requirements. • System testing is a blend of functional (black-box) and structural (white-box) testing - - - testing mostly “main” threads of system behavior.

2. Thread • A thread is a sequence of activities that are observable. • There are many levels of granularity for a thread: • A sequence of instructions as in a DU-pathfor unit test • A flow of control among a set of related modules as in a MM-path in an integration path. • A sequence of “atomic” functionsthat contributes to the accomplishment of a major functionality as described in a requirements specification. • In system testing, we are interested in the • a) high-level (cross-functional) threadsand • b) “multiple” threads.

3. Examples of threads from the ATM Problem (p27 of the text) Unit Testing • Entry of a digit: (port entry of a numerical digit keystroke and a port out of a digit echo on the screen. • This is a minimal “atomic system function” and qualifies as a thread of interest at the unit test level. • Entry of a PIN number: (this entails a set of activities from screen request of a PIN with interleaved sequence of digit entry until completion - - - possibly including cancellation and up to three re-tries). • This is a sequence of atomic system functions that also qualifies as athread, probably fit for integration testingor unit testing levels. • A simple ATM transaction: (this includes a set of functions such as 1) Card entry, 2) PIN entry, 3) choice of transaction type (deposit, withdraw, account detail processing, etc.) • This is a sequence of atomic system functions that is a thread&accomplishes a major function, fit for integration testing orsystem testinglevels . • Multiple ATM transactions: (this includes a complete user session where several different transactions- - - query, withdraw, deposit of different accounts - - - may transpire.) • This is a sequence of different/multiple threadsand is definitely in the domain of system testing. System Testing

4. Some definitions related to thread • An atomic system function (ASF)is an action that is observable at the system level in terms of port entry and port output. • An ASF graphis a directed graph of a ASF represented system where the nodes are the ASF’s and the edges represent the sequential flow. • A source ASFis an ASF that is a source node in an ASF graph. • A sink ASFis an ASF that is a sink node in an ASF graph. • A system threadis a path from a source ASF to a sink ASF in the ASF graph of the system. • The thread graph of a systemis a directed graph where the • a) nodes are the threads of the system and • b) the edges represent the sequential execution flow from one thread to another.

5. Requirements Specification for System Testing • Requirements specification served as a tool (input) for, mainly black-box testing, but also white-box testing even at the unit testing level; it is even more important as a source of developing test cases for system testing. • There are many ways to express requirements and many ways to view the specification. As a whole the requirements specification may be viewed a set of inter-related elements (“basis” for requirements): • Data (information and information structure) • Actions (functional tasks) • Devices(for input, output, and storage) • Events (triggers and combination of action and data) • Threads (business flow or process flow, involving events) Only thing missing is the non-functional attributesuch as quality, performance, etc.

6. Multiple Ways of Viewing Specification “Basis” elements Used mostly for early spec and development of system devices Data Contextual model Actions Behavior model Devices Often used for requirements specifications Events Structural model Threads Used mostly for development There are many tools for expressing these models: (e.g.) - state transition diagram ( or Finite State Machine) - E-R diagram - Petri net

7. Using Finite State Machine or State Transition Diagram Welcome Card entry (state A) State Input Next State Output A correct card B screen 2 A bad card A screen 1; card B good pin # C screen 5 B failed pin # A screen 4 wrong card Display screen 1; Eject card Correct card Display screen 2 Pin Entry (state B) Failed Pin Process Display screen 4 Successful Pin Process Tabular form Display screen 5 Choosing Transaction (state C) Graphical form

8. Finite State Machine at a “deeper” level for PIN processing Welcome Card entry (state A) Incorrect Pin/ cancel wrong card Display screen 4, 1 Display screen 1; Eject card Correct card Display screen 2 1st Pin Entry (state B) Incorrect Pin/ cancel 2nd Pin Entry (state D) Incorrect Pin/ cancel 3rd Pin Entry (state E) Display screen 3, 2 Successful Pin Process Display screen 3, 2 Correct Pin Display screen 5 Choosing Transaction (state C) Display screen 5 Correct Pin Display screen 5

9. Threads with Finite State Machine • If we can model the requirements specifications with the finite state machine model, then: • A set of transitions (with inputs and outputs) can be a source of threads for system test because it covers: • Events ( state and input) • Action (state transition and output) • Data (inputs and outputs) • Thread (series of state transitions) • The drawbacks are: • that not all specifications “easily” fit this model • that the determination of what depth levelshould the finite state machine be for system test; very low a level is more appropriate for unit or integration test

10. Test Coverage Metrics with Finite State Machine • Every node (state) is covered. • This is a very minimal coverage, much like every statement is covered (recall this from structural path testing) • In our 1st state transition chart - - - this is equivalent to covering states A, B, and C with correct card and successful PIN processing. • Every node and edge (transition) is covered • This is a more complete coverage if the finite state machine is carried to deep enough level.

11. Strategies for Thread Testing Finite State Machine modeled systems • Event based (state-input based): • Each input event occurs • A “typical” or “common” sequence of input events occur • Each input event occurs in every “relevant” data context • For a given context, all “inappropriate” input events occur • For a given context, all possible (both appropriate & inappropriate) inputs events occur • Event based (state-output based): • Each output event occurs • Each output event occurs for every “cause” • Port-based (both input and output): • Cover all input and out ports

12. Strategies for thread Testing Data Represented Systems • Some software system requirements are better represented with E-R diagram. • For E-R modeling used for specifications, the threads may be identified via: • Looking at the cardinality of every relationship • One-one • One-many • Many-one • Many - many • Looking at the participation factor of every relationship • Looking at functional dependenciesamong relationships • e.g. loaning a book that’s not available More importantly --- we want to make sure that the DB “access” is tested, along with threads such as a) shutdown -restartb) backup-recovery c) multiple access threads

13. Using Operational Profile when interested in“Effectiveness” • The effectiveness of testing is often measured in terms of problems found versus effort spent or • (# of defects found) / person hours spent • (# of defects found) / number of test cases • Historically, most of the failures also tend to fall in small parts of the system (80% failures occur in 20% of the system - - - e.g. the most heavily traversed threads). • Thus if we can collect the operational profilesof the users, we can identify the most heavily used threads. • Thisstrategy of system testing with operational profile can improve our test efficiency. Not just the number of problems found

14. User-Operational Profile Example(naïve user versus experienced user) (20/20) (20/20) prob = .25 √ term naïve users (20/80) default f1 f4 (5/5) prob = .063 (5/10) f4 term Start (80 users) (5/10) (5/5) prob = .063 (10/60) f1 f6 term experienced users (60/80) (40/40) (40/40) (40/60) prob = .50√√ term f7 f2 Choice of f1,f2,f3 (10/60) (3/10) (3/3) prob = .037 term f4 f3 (7/10) (7/7) prob = .087 f5 Note that 2 usage cases take up 75% of operational profile ! term

15. Software changesand Regression Test • In the life span of a software, we can anticipate changes that result in multiple cycles of fixes and release. Thus it needs to be retested to ensure that what worked before still works (did not get regressed). • A common strategy is to re-run the complete system test over as the regression test • A more economical strategy for regression test is to develop (1) new threads for the new areas and(2) only include those old threads that are affected by the new release. (Yes, there may be an element of risk) Think about the “neighborhood” testing strategy-last lecture