1. CSEB233 Fundamentals of Software Engineering
Module 6: Software Verification and Validation
Badariah Solemon 2011

2. Objectives
To introduce the fundamental concepts of software verification and validation
To explain how to conduct software testing and when to stop
To discuss several types of testing: unit testing, integration testing, validation testing, and system testing
To introduce the standard for software test documentation
To introduce a set of techniques for the creation of test cases that meet overall testing objectives and the testing strategies
Badariah Solemon 2011

3. Verification & Validation
Is a whole software engineering process
V & V must be applied at each framework activity in the software process.
Verification refers to the set of tasks that ensure that software correctly implements a specific function.
Validation refers to a different set of tasks that ensure that the software that has been built is traceable to customer requirements. Boehm [Boe81] states this another way:
Verification: "Are we building the product right?"
Validation: "Are we building the right product?”
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4. Verification & Validation(cnt’d)
Has two principal objectives:
Discover defects in a system;
Assess whether or not the system is useful and useable in an operational situation.
V&V should establish confidence that the software is fit for purpose.
This does NOT mean completely free of defects.
Rather, it must be good enough for its intended use and the type of use will determine the degree of confidence that is needed.
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5. Verification & Validation(cnt’d)
V & V activities include:
Technical reviews
Quality and configuration audits
Performance monitoring
Simulation
Feasibility study
Documentation review
Database review
Algorithm analysis
Development testing
Qualification testing
Acceptance testing
Installation testing
SQA activities*
Testing
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6. requirements conformance
Software Testing
The process of exercising a program with the specific intent of finding errors prior to delivery to the end user.
Must be planned carefully to avoid wasting development time and resources, and conducted systematically .
What testing shows?
errors
requirements conformance
performance
an indication
of quality
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7. Who Tests the Software? developer independent tester
Understands the system
Must learn about the system,
but, will test "gently"
but, will attempt to break it
and, is driven by "delivery"
and, is driven by quality
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8. Who Tests the Software?(cnt’d)
Misconceptions :
The developer should do no testing at all
Software should be “tossed over the wall” to stranger who will test it mercilessly
Testers are not involved with the project until it is time for it to be tested
The developer and Independent Test Group (ITG) must work together throughout the software project to ensure that thorough tests will be conducted.
An ITG does not have the “conflict of interest” that the software developer might experience.
While testing is conducted, the developer must be available to correct errors that are uncovered.
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9. Testing Strategy
Identifies steps to be undertaken, when these steps are undertaken, how much effort, time, and resources will be required.
Any testing strategy must incorporate:
Test planning
Test case design
Test execution
Resultant data collection and evaluation
Should provide guidance for the practitioners and a set of milestones for the manager.
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10. Testing Strategy (cnt’d)
Generic characteristics of software testing strategies that have been proposed in the literature:
To perform effective testing, you should conduct effective technical reviews.
By doing this, many errors will be eliminated before testing commences.
Testing begins at the component level and works "outward" toward the integration of the entire computer-based system.
Different testing techniques are appropriate for different software engineering approaches and at different points in time.
Testing is conducted by the developer of the software and (for large projects) an independent test group.
Testing and debugging are different activities, but debugging must be accommodated in any testing strategy.
Badariah Solemon 2011

11. Overall Software Testing Strategy
Maybe viewed in the context of the spiral.
Begins by ‘testing-in-the-small’ and move toward ‘testing-in-the-large’
System engineering
Analysis modeling
Design modeling
Code generation
Unit testing
Integration testing
Validation testing
System testing
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12. Overall Software Testing Strategy (cnt’d)
Unit Testing
focuses on each unit of the software (e.g., component, module, class ) as implemented in source code
Integration Testing
focuses on issues associated with verification and program construction as components begin interacting with one another
Validation Testing
provides assurance that the software validation criteria (established during requirements analysis) meets all functional, behavioral, and performance requirements
System Testing
verifies that all system elements mesh properly and that overall system function and performance has been achieved
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13. Unit Testing Focuses on assessing:
internal processing logic and data structures within the boundaries of a component (module).
proper information flow of module interfaces.
local data to ensure that integrity is maintained.
boundary conditions.
basis (independent) path.
all error handling paths.
If resources are scarce to do comprehensive unit testing, select critical or complex module and unit test only those.
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14. Unit Testing (cnt’d) module to be tested results software engineer
boundary conditions
error handling paths
independent paths
local data structures
interface
software
engineer
test cases
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15. Integration Testing
After unit testing of individual modules the modules are combined together into a system.
Question commonly asked once all modules have been unit tested:
“If they work individually, why do you doubt that they’ll work when we put them together?”
The problem is “putting them together” – interfacing. Examples:
Data can be loss across an interface
Global data structures can present problems
Subfunctions, when combined, may not produce the desired function
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16. Integration Testing (cnt’d)
Incremental integration testing strategies:
Bottom-up integration
Top – down integration
Regression testing
Smoke testing
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17. Bottom-up Integration
An approach where the lowest level modules are tested first, then used to facilitate the testing of higher level modules.
The process is repeated until the module at the top of the hierarchy is tested.
Top level modules are the most important yet tested last.
Is helpful only when all or most of the modules of the same development level are ready.
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18. Bottom-up Integration (cnt’d)
The steps:
Test D, E individually (using a dummy program called ‘driver’)
Low-level components are combined into clusters that perform a specific software function.
Test C such that it call D (If an error occurs we know that the problem is in C or in the interface between C and D)
Test C such that it call E (If an error occurs we know that the problem is in C or in the interface between C and E)
The cluster is tested.
Drivers are removed and clusters are combined moving upward in the program structure. B F G
drivers are replaced one at a
time, "depth first" C
‘worker modules’ are grouped into
builds and integrated D E
cluster
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19. Top-down Integration The steps:
Main/top module used as a test driver and stubs are substitutes for modules directly subordinate to it.
Subordinate stubs are replaced one at a time with real modules (following the depth-first or breadth-first approach).
Tests are conducted as each module is integrated.
On completion of each set of tests and other stub is replaced with a real module.
Regression testing may be used to ensure that new errors not introduced.
The process continues from step 2 until the entire program structure is built
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20. Top-down Integration (cnt’d)
Example steps:
Test A individually (use stubs for other modules)
Depending on the integration approach selected, subordinate stubs are replaced one at a time with actual components
In a ‘depth-first’ structure:
Test A such that it calls B (use stub for other modules)
If an error occurs we know that the problem is in B or in the interface between A and B
Replace stubs one at a time, ‘depth-first’ and re-run tests A
top module is
tested with stubs B F G
stubs are replaced one at
a time, "depth first" C
as new modules are integrated,
some subset of tests is re-run D E
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21. Regression Testing Focuses on retesting after changes are made
Whenever software is corrected, some aspect of the software configuration (the program, its documentation, or the data that support it) is changed.
Regression testing helps to ensure that changes (due to testing or for other reasons) do not introduce unintended behavior or additional errors.
In traditional regression testing, we reuse the same tests.
In risk-oriented regression testing, we test the same areas as before, but we use different (increasingly complex) tests.
Regression testing may be conducted manually, by re-executing a subset of all test cases or using automated capture/playback tools.
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22. Smoke Testing
A common approach for creating “daily builds” for product software
Smoke testing steps:
Software components that have been translated into code are integrated into a “build.”
A build includes all data files, libraries, reusable modules, and engineered components that are required to implement one or more product functions.
A series of tests is designed to expose errors that will keep the build from properly performing its function.
The intent should be to uncover “show stopper” errors that have the highest likelihood of throwing the software project behind schedule.
The build is integrated with other builds and the entire product (in its current form) is smoke tested daily.
The integration approach may be top down or bottom up.
Badariah Solemon 2011

23. Validation Testing
Focuses on uncovering errors at the software requirements level.
SRS might contain a ‘Validation Criteria’ that forms the basis for a validation-testing approach
Validation-Test Criteria:
Ensure that:
all functional requirements are satisfied,
all behavior characteristics are achieved,
all content is accurate and properly presented,
all performance requirements are attained, documentation is correct, and
usability and other requirements are met.
Badariah Solemon 2011

24. Validation Testing (cnt’d)
An important element of the validation process is a configuration review/audit
Ensure that all elements of the software configuration have been properly developed, are cataloged, and have the necessary detail to strengthen the support activities.
A series of acceptance tests are conducted to enable the customer to validate all requirements
To make sure the software works correctly for intended user in his or her normal work environment.
Alpha test – version of the complete software is tested by customer under the supervision of the developer at the developer’s site
Beta test – version of the complete software is tested by customer at his or her own site without the developer being present
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25. System Testing
A series of different tests to verify that system elements have been properly integrated and perform allocated functions.
Types of system tests:
Recovery Testing
Security Testing
Stress Testing
Performance Testing
Deployment Testing
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26. System Testing (cnt’d)
Recovery Testing
forces the software to fail in a variety of ways and verifies that recovery is properly performed
Security Testing
verifies that protection mechanisms built into a system will, in fact, protect it from improper penetration
Stress Testing
executes a system in a manner that demands resources in abnormal quantity, frequency, or volume
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27. System Testing (cnt’d)
Performance Testing
test the run-time performance of software within the context of an integrated system
Deployment Testing
examines all installation procedures and specialized installation software that will be used by customers, and
all documentation that will be used to introduce the software to end users.
Badariah Solemon 2011

28. Software Test Documentation
IEEE Standard for Software Test Documentation
IEEE standard that specifies the form of a set of documents for use in eight defined stages of software testing
The documents are:
Test Plan
Test Design Specification
Test Case Specification
Test Procedure Specification
Test Item Transmittal Report
Test Log
Test Incident Report
Test Summary Report
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29. Software Test Documentation (cnt’d)
Test Plan: a management planning document that shows:
How the testing will be done (including SUT (system under test) configurations).
Who will do it
What will be tested
How long it will take (although this may vary, depending upon resource availability).
What the test coverage will be, i.e. what quality level is required
Test Design Specification:
detailing test conditions and the expected results as well as test pass criteria.
Badariah Solemon 2011

30. Software Test Documentation (cnt’d)
Test Procedure Specification:
detailing how to run each test, including any set-up preconditions and the steps that need to be followed
Test Item Transmittal Report:
reporting on when tested software components have progressed from one stage of testing to the next
Test Log:
recording which tests cases were run, who ran them, in what order, and whether each test passed or failed
Test Incident Report:
detailing, for any test that failed, the actual versus expected result, and other information intended to throw light on why a test has failed.
Badariah Solemon 2011

31. Software Test Documentation (cnt’d)
Test Summary Report:
A management report providing any important information uncovered by the tests accomplished, and including assessments of the quality of the testing effort, the quality of the software system under test, and statistics derived from Incident Reports.
The report also records what testing was done and how long it took, in order to improve any future test planning.
This final document is used to indicate whether the software system under test is fit for purpose according to whether or not it has met acceptance criteria defined by project stakeholders.
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32. Test-case Design
Focuses on a set of techniques for the creation of test cases that meet overall testing objectives and the testing strategies.
These techniques provide a systematic guidance for designing tests that
Exercise the internal logic and interfaces of every software component/module
Exercise the input and output domains of the program to uncover errors in program function, behaviour, and performance.
Badariah Solemon 2011

33. Test-case Design (cnt’d)
For conventional application, software is tested from two perspectives:
‘White-box’ testing
focus on the program control structure (internal program logic).
Test cases are derived to ensure that all statements in the program have been executed at least once during testing and all logical conditions have been exercised.
Performed early in the testing process
‘Black-box’ testing
Examines some fundamental aspect of a system with little regard for the internal logical structure of the software
Performed during later stages of testing
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34. White-box Testing
Using white-box testing method, you may derive test-cases that:
Guarantee that al independent paths within a module have been exercised at least once
Exercise all logical decisions on their true and false sides
Execute all loops at their boundaries and within their operational bounds
Exercise internal data structures to ensure their validity
Example method: basis path testing.
Badariah Solemon 2011

35. White-box Testing(cnt’d)
Basis path testing:
Test cases derived to exercise the basis set are guaranteed to execute every statement in the program at least one time during testing
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36. Deriving Test Cases
Steps to derive the test cases (by applying the basis path testing method):
Using the design or code, draw a corresponding flow graph.
The flow graph depicts logical control flow using the notation illustrated in next slide.
Refer Figure 18.2 in page comparison between a flowchart and a flow graph
Calculate the Cyclometic Complexity V(G) of the flow graph
Determine a basis set of independent paths
Prepare test cases that will force execution of each path in the basis set.
Badariah Solemon 2011

37. Deriving Test Cases (cnt’d)
Flow graph notation:
UNTIL
Sequence IF IF
CASE
WHILE
Badariah Solemon 2011

38. Drawing Flow Graph: Example 1
Predicate nodes
void foo (float y, float a *, int n) {
float x = sin (y) ;
if (x > 0.01)
z = tan (x) ;
else
z = cos (x) ;
for (int i = 0 ; i < x ; + + i)
a[i] = a[i] * z ;
Cout < < a [i]; } 1 1 2 R1 3 2 3 4
Predicate nodes R3 5 6 5 R2 7 6 8 8 7
Badariah Solemon 2011

39. Drawing Flow Graph: Example 2
Predicate nodes
void foo (float y, float a *, int n) {
float x = sin (y) ;
if (x > 0.01)
z = tan (x) ;
else
z = cos (x) ;
for (int i = 0 ; i < x ; + + i)
a[i] = a[i] * z ;
Cout < < a [i]; } 1 1 2 R1 3 2 3 4
Predicate nodes R3 5 6 5 R2 7
6,7 8 8
Badariah Solemon 2011

40. Drawing Flow Graph: Example 3
See Figure 18.2 in page 486
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41. Deriving Test Cases (cnt’d)
The arrows on the flow graph, called edges or links, represent flow of control and are analogous to flowchart arrows.
Area bounded by edges and nodes are called regions.
When counting regions, we include the area outside the graph as region.
Region 4
edges
Region 6
Region 5
Region 3
Region 1
Region 2
Badariah Solemon 2011

42. Deriving Test Cases: Example 1
Step 1: Draw a flow graph
Predicate nodes
Predicate nodes
Predicate nodes R2 R1 R3 R4
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43. Deriving Test Cases: Example 1 (cnt’d)
Step 2: Calculate the Cyclomatic complexity, V(G)
Cyclomatic complexity can be used to count the minimum number of independent paths.
A number of industry studies have indicated that the higher V(G), the higher the probability or errors.
The SEI provides the following basic risk assessment based on the value of code:
Cyclomatic Complexity
Risk Evaluation
1 to 10
a simple program, without very much risk
11 to 20
a more complex program, moderate risk
21 to 50
a complex, high risk program
> 50
an un-testable program (very high risk)
Badariah Solemon 2011

44. Deriving Test Cases: Example 1 (cnt’d)
Ways to calculate V(G):
V(G) = the number of regions of the flow graph.
V(G) = E – N + 2 ( Where “E” are edges & “N” are nodes)
V(G) = P + 1 (Where P is the predicate nodes in the flow graph, each node that contain a condition)
Example:
V(G) = Number of regions = 4
V(G) = E – N + 2 = 16 – = 4
V(G) = P + 1 = = 4
Badariah Solemon 2011

45. Deriving Test Cases: Example 1 (cnt’d)
Step 3: Determine a basis set of independent paths
Path 1: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 14
Path 2: 1, 2, 3, 4, 5, 14
Path 3: 1, 2, 3, 4, 5, 6, 7, 11, 12, 5, …
Path 4: 1, 2, 3, 4, 6, 7, 2, 11, 13, 5, …
Step 4: Prepare test cases
Test cases should be derived so that all of these paths are executed
A dynamic program analyser may be used to check that paths have been executed
Badariah Solemon 2011

46. Deriving Test Cases: Example 2
Refer pages 486 – 488
* Other topics related to testing conventional application such as control structure testing, black-box testing, model-based testing , patterns for software testing are described in pages
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47. When to Stop Testing? According to Pan (1999):
Testing is potentially endless.
We can not test till all the defects are unearthed and removed -- it is simply impossible.
At some point, we have to stop testing and ship the software. The question is when.
According to Pan (1999):
Realistically, testing is a trade-off between budget, time and quality.
It is driven by profit models.
Badariah Solemon 2011

48. When to Stop Testing?(cnt’d)
The pessimistic, and unfortunately most often used approach is to stop testing whenever some, or any of the allocated resources -- time, budget, or test cases -- are exhausted.
The optimistic stopping rule is to stop testing when either reliability meets the requirement, or the benefit from continuing testing cannot justify the testing cost.
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49. Summary
Software testing plays an extremely important role in V&V, but many other SQA activities are also necessary.
Testing must be planned carefully to avoid wasting development time and resources, and conducted systematically.
The developer and ITG must work together throughout the software project to ensure that thorough tests will be conducted.
The software testing strategy is to begins by ‘testing-in-the-small’ and move toward ‘testing-in-the-large’
The IEEE standard specifies a set of documents for use in eight defined stages of software testing.
The ‘white-box’ and ‘black-box’ techniques provide a systematic guidance for designing test cases.
We need to know when is the right time to stop testing.
Badariah Solemon 2011

50. References and credit
Contents in the slides are adapted from the book and the slides that accompanied the book by R.S. Pressman, Software Engineering: A Practitioner’s Approach, 7th. Edition, McGraw Hill, 2009.
Pan, J. (1999). Software Testing. Retrieved 25th January 2011 from
Badariah Solemon 2011