Ian Sommerville, Software Engineering, 9th EditionCh 8

Chapter 8 – Software Testing
1Chapter 8 Software testing
Note: These are a modified version of Ch 8 slides available from the
author’s site http://www.cs.st-andrews.ac.uk/~ifs/Books/SE9/
Ian Sommerville,
Software Engineering, 9th
Edition
Pearson Education, Addison-Wesley
CS 425 November 1, 2010

Topics covered
 Development testing
 Test-driven development
 Release testing
 User testing

Program testing
 Testing shows that a program does what it is intended to do
and to discover program defects before it is put into use. It is
a dynamic validation technique.
 To test, you execute a program using artificial data.
 Check the results of the test run for errors, anomalies or
information about the program’s non-functional attributes.
 Can reveal the presence of errors NOT their absence.
 Testing is part of a more general verification and validation
process, which also includes static validation techniques.
Chapter 8 Software testing 3

Testing goals
 To demonstrate that software meets its requirements.
 For custom software, at least one test for every requirement in
the requirements document.
 For generic software products, have tests for all of the system
features AND feature combinations.
 To discover situations in which the behavior of the
software is incorrect or undesirable.
 Defect testing is concerned with rooting out undesirable system
behavior such as system crashes, unwanted interactions with
other systems, incorrect computations and data corruption.

Validation and defect testing
 The first goal leads to validation testing
 You expect the system to perform correctly using a given set of
test cases that reflect the system’s expected use.
 The second goal leads to defect testing
 The test cases are designed to expose defects. Tests can be
obscure and address unusual use of software.

Testing process goals
 Validation testing
 To demonstrate to the developer and the system customer that
the software meets its requirements
 A successful test shows that the system operates as intended.
 Defect testing
 To discover faults or defects in the software where its behaviour
is incorrect or doesn’t follow its specification
 A successful test is a test that makes the system perform
incorrectly.
(Dijkstra et al., 1972):Testing can only show the presence
of errors, not their absence

An input-output model of program testing

 Verification:
"Are we building the product right?”
 The software should conform to its specification. Meets the SW
documented requirements.
 Validation:
"Are we building the right product?”
 The software should do what the user really requires. Meets the
customer expectations.
Verification vs validation

V & V confidence
 Aim of V & V is to establish confidence that the system is
‘fit for purpose’.
 The level of confidence Depends on:
 Software purpose
• The level of confidence depends on how critical the software is to an
organization.
 User expectations
• Users may have low expectations of certain kinds of software.
 Marketing environment
• Getting a product to market early may be more important than
finding defects in the program.

 Software inspections: Analyze the static system
representation to discover problems (static
verification)
 May be supplemented by tool-based document and code
analysis (discussed in Chapter 15).
 Software testing: Exercise and observe product
behaviour (dynamic verification)
 The system is executed with test data and its operational
behaviour is observed.
Inspections and testing

The arrows indicate the stages in the process where the techniques may be used.

Software inspections
 People examine the source code to discover anomalies
and defects.
 Inspections do not require execution of a system.
 They may be applied to any representation of the system
(requirements, design, configuration data, test data, etc.)
 They have been shown to be an effective technique for
discovering program errors.

Software Inspections
http://weblog.bosslogic.com/2007/07/formal-
inspection-an-introduction/

Advantages of inspections
 During testing, errors can mask (hide) other errors.
Because inspection is a static process, you don’t have to
be concerned with interactions between errors.
 Incomplete versions of a system can be inspected
without additional costs. If a program is incomplete, then
you need to develop specialized test harnesses to test
the parts that are available.
 As well as searching for program defects, an inspection
can also consider broader quality attributes of a
program, such as compliance with standards, portability
and maintainability.

 Inspections and testing are complementary and not
opposing verification techniques.
 Both should be used during the V & V process.
 Inspections can check conformance with a specification
but not conformance with the customer’s real
requirements.
 Inspections cannot check non-functional characteristics
such as performance, usability, etc.
 Inspection are not good for discovering defects that arise
because of unexpected interactions between different
parts of a program, timing problems.

Stages of testing
Typically, a commercial software system has to go through
three stages of testing:
 Development testing; the system is tested during
development.
 Release testing; a separate testing team tests a
complete version of the system before it is released.
 User testing, where users or potential users of a system
test the system in their own environment.

8.1 Development testing
 Development testing; includes all testing activities that
are carried out by the developers.
 Unit testing, Focuses on testing the functionality of objects or
methods.
 Component testing, create components from object
combinations. Focuses on testing component interfaces.
 System testing, the components in a system are integrated and
the system is tested as a whole. Focuses on testing component
interactions.

8.1.1 Unit testing
 Unit testing is the process of testing individual
components in isolation.
 The purpose is to discover defects
 Units may be:
 Individual functions or methods within an object
 Object classes with several attributes and methods
 Composite components with defined interfaces used to access
their functionality.

Object class testing
 Complete test coverage of a class involves
 Testing all operations associated with an object
 Setting and interrogating all object attributes
 Exercising the object in all possible states.
 Inheritance makes it more difficult to design object class
tests.

The weather station object interface

Weather station testing
 Need to define test cases for all operations.
 Using a state model, identify sequences of state
transitions to be tested and the event sequences to
cause these transitions
 For example:
 Shutdown -> Running-> Shutdown
 Configuring-> Running-> Testing -> Transmitting -> Running
 Running-> Collecting-> Running-> Summarizing -> Transmitting
-> Running

The Weather Station Testing Object

Automated testing
 Whenever possible, unit testing should be automated so
that tests are run and checked without manual
intervention.
 In automated unit testing, you make use of a test
automation framework (such as JUnit) to write and run
your program tests.
https://www.youtube.com/watch?v=I8XXfgF9GSc
Or online:
http://www.tutorialspoint.com/junit/junit_environment_setup.htm
 Unit testing frameworks can run all of the tests you
implemented and report on the success of the tests.

Automated Testing

8.1.2 Choosing unit test cases
Unit test effectiveness
 The test cases should show that component does what it
is supposed to do.
 Should reveal defects in the component, if there are any.
 This leads to 2 types of unit test cases:
 Tests that reflect normal operation of a program to show that the
meets expectations.
 Tests based on testing experience of where common problems
arise. Should use abnormal inputs, check that these are properly
processed, and not crash the component.

Testing strategies
 Partition testing, where you identify groups of inputs that
have common characteristics and should be processed
in the same way.
 You should choose tests from within each of these groups.
 Guideline-based testing, where you use testing
guidelines to choose test cases.
 These guidelines reflect previous experience of the kinds of
errors that programmers often make when developing
components.

Partition testing
 Input data and output results often fall into different
classes where all members of a class are related.
 Each of these classes is an equivalence partition or
domain where the program behaves in an equivalent
way for each class member.
 Test cases should be chosen from each partition.

Equivalence partitioning

Example
For example, say a program specification states that the
program accepts 4 to 10 inputs which are five-digit
integers greater than 10,000. You use this information to
identify the input partitions and possible test input
values. These are shown in Figure 8.6.

Equivalence partitions

Testing guidelines (sequences, lists, arrays)
 Test software with sequences which have only a single
value.
 Use sequences of different sizes in different tests.
 Derive tests so that the first, middle and last elements of
the sequence are accessed.
 Test with sequences of zero length.

General testing guidelines
 Choose inputs that force the system to generate all error
messages
 Design inputs that cause input buffers to overflow
 Repeat the same input or series of inputs numerous
times
 Force invalid outputs to be generated
 Force computation results to be too large or too small.

Path Testing (Wight box testing)
http://users.csc.calpoly.edu/~jdalbey/206/Lectures/BasisPathTutorial/
1.3.1 Flow Graph Notation
Notation for representing control flow
On a flow graph:
Arrows called edges represent flow of control
Circles called nodes represent one or more
actions.
Areas bounded by edges and nodes
called regions.
A predicate node is a node containing a
condition Chapter 8 Software testing 33

Example

Cyclomatic Complexity
The cyclomatic complexity gives a quantitative measure of the logical complexity.

 Example has:
 Independent Paths:
 1, 9
 1, 2, 3, 8, 1, 9
 1, 2, 4, 5, 7, 8, 1, 9
 1, 2, 4, 6, 7, 8, 1, 9
 Cyclomatic Complexity of 4; computed using any of these 3
formulas:
1. #Edges - #Nodes + #terminal vertices (usually 2)
2. #Predicate Nodes + 1
3. Number of regions of flow graph.
 Cyclomatic complexity provides upper bound for number of tests
required to guarantee coverage of all program statements.Chapter 8 Software testing 37

8.1.3 Component testing (Stop)
 Software components are often composite components
that are made up of several interacting objects.
 Functionality of a component is accessed through a
defined interface.
 Focus on showing that the component interface behaves
according to its specification.
 Assume that unit tests on the individual objects within the
component have been completed.

Interface testing

Interface testing
 Objectives are to detect faults due to interface errors or
invalid assumptions about interfaces (conflicts with
specification).
 Interface types
 Parameter interfaces Data passed from one method or
procedure to another. (function call)
 Shared memory interfaces Block of memory is shared between
procedures or functions. (e.g. parallel threads memory pools,
empadded systems)
 Procedural interfaces Sub-system encapsulates a set of
procedures to be called by other sub-systems. Objects and
reusable components have this form of interface.
 Message passing interfaces Sub-systems request services from
other sub-systems (client-server, web browser) 40Chapter 8 Software testing

Interface errors
 Interface misuse
 A calling component calls another component and makes an
error in its use of its interface e.g. parameters in the wrong order
or wrong number of parameters.
 Interface misunderstanding
 A calling component embeds assumptions about the behaviour
of the called component which are incorrect. (assume div by
zero will be handled elegantly, FName?, binary search with
unordered files)
 Timing errors
 The called and the calling component operate at different
speeds and out-of-date information is accessed.

Interface testing guidelines
 Design tests so that parameters to a called procedure
are at the extreme ends of their ranges.
 Always test pointer parameters with null pointers.
 Design tests which cause the component to fail.
 Use stress testing in message passing systems.
 In shared memory systems, vary the order in which
components are activated.( some assumes specific
order while it is not always true)

8.1.4 System testing
 System testing during development involves integrating
components to create a version of the system and then
testing the integrated system.
 The focus is testing interactions between components.
 Checks that components are compatible, interact
correctly and transfer data correctly across their
interfaces.
 Tests the emergent behavior (behavior not explicitly
described by the components, and is unexpected)

System Testing: Emergent Behavior
 http://www.amazon.com/Turtles-Termites-Traffic-Jams-Explor

System and component testing
Overlaps but
 Reusable components that have been separately
developed AND off-the-shelf systems may be integrated
with newly developed components. The complete
system is then tested.
 Components developed by different team members or
sub-teams may be integrated at this stage. System
testing is a collective rather than an individual process.
 In some companies, system testing may involve a separate
testing team with no involvement from designers and
programmers.

Use-case testing
Because of its focus on interactions, use case–based
testing is an effective approach to system testing.
 The use-cases developed to identify system interactions
can be used as a basis for system testing.
 Each use case usually involves several system
components so testing the use case forces these
interactions to occur.
 The sequence diagrams associated with the use case
documents the components and interactions that are
being tested.

Use-case testing
http://andrewtokeley.net/archive/2008/03/24/enterprise-architect-for-testers.aspx

Testing policies
 Exhaustive system testing is impossible so testing
policies which define the required system test coverage
may be developed.
 Examples of testing policies:
 All system functions that are accessed through menus should be
tested.
 Combinations of functions (e.g. text formatting) that are
accessed through the same menu must be tested.
 Where user input is provided, all functions must be tested with
both correct and incorrect input.

8.2 Test-driven development
 Test-driven development (TDD) is an approach to
program development in which you create tests before
writing code.
 You develop code incrementally, along with a test for
that increment. You don’t move on to the next increment
until the code that you have developed passes its test.
 TDD was introduced as part of agile methods such as
Extreme Programming. However, it can also be used in
plan-driven development processes.

Test-driven development

TDD process activities
1. Start by identifying the increment of functionality that is
required. This should normally be small and
implementable in a few lines of code.
2. Write a test for this functionality and implement this as
an automated test.
3. Run the test, along with all other tests that have been
implemented. Initially, you have not implemented the
functionality so the new test will fail.
4. Implement the functionality and re-run the test.
5. Once all tests run successfully, you move on to
implementing the next chunk of functionality.

Benefits of test-driven development
 Code coverage
 Every code segment that you write has at least one associated
test so all code written has at least one test.
 Regression testing
 A regression test suite is developed incrementally as a program is
developed. You can always run regression tests to check that changes to
the program have not introduced new bugs.
 Simplified debugging
 When a test fails, it should be obvious where the problem lies.
The newly written code needs to be checked and modified.
 System documentation
 The tests themselves are a form of documentation that describe
what the code should be doing. 52Chapter 8 Software testing

Regression testing
 Regression testing is testing the system to check that
changes have not ‘broken’ previously working code.
 Manual regression testing is expensive
 Automated regression testing is simple and
straightforward.
 All tests are rerun every time a change is made to the
program.
 Tests must run ‘successfully’ before the change is
committed.

8.3 Release testing
 Release testing is the process of testing a particular release
of a system.
 The primary goal is to convince the supplier of the system
that it is good enough for release.
 Release testing, therefore, has to show that the system delivers its
specified functionality, performance and dependability, and that it
does not fail during normal use.
 Usually a black-box testing process where tests are only
derived from the system specification.

Release testing and system testing
 Forms of release testing:
 Requirements-based testing
 Scenario-based testing
 Release testing is a form of system testing.
 Important differences:
 A separate team that has not been involved in the system
development, should be responsible for release testing.
 System testing by the development team should focus on
discovering bugs in the system (defect testing). The objective of
release testing is to check that the system meets its requirements
and is good enough for external use (validation testing).

8.3.1 Requirements based testing
 Requirements-based testing involves examining
each requirement and developing a test or tests
for it.

8.3.2 Scenario testing
 A scenario is a story that describes one way in which the
system might be used.
 Scenarios should be realistic.
 Scenario testing is an approach to release testing where
you devise typical scenarios of use and use these to
develop test cases for the system.

8.3.3 Performance testing
 Test the emergent properties of a system, such as
performance and reliability.
 Tests should reflect the profile of use of the system.
 Performance tests usually involve planning a series of
tests where the load is steadily increased until the
system performance becomes unacceptable.
 Stress testing is a form of performance testing where the
system is deliberately overloaded to test its failure
behavior.

8.4 User testing
 User or customer testing is a stage in the testing process
in which users or customers provide input and advice on
system testing.
 User testing is essential, even when comprehensive
system and release testing have been carried out.
 The reason for this is that influences from the user’s working
environment have a major effect on the reliability, performance,
usability and robustness of a system. These cannot be
replicated in a testing environment.

Types of user testing
 Alpha testing
 Users of the software work with the development team to test the
software at the developer’s site.
 Beta testing
 A release of the software is made available to users to allow
them to experiment and to raise problems that they discover with
the system developers.
 Acceptance testing
 Customers test a system to decide whether or not it is ready to
be accepted from the system developers and deployed in the
customer environment. Primarily for custom systems.

Key points
 Testing can only show the presence of errors in a
program. It cannot demonstrate that there are no
remaining faults.
 Development testing is the responsibility of the software
development team. A separate team should be
responsible for testing a system before it is released to
customers.
 Development testing includes unit testing, component
testing, and system testing.

Key points
 When testing software, you should try to ‘break’ the software by
using experience and guidelines to choose types of test case that
have been effective in discovering defects in other systems.
 Wherever possible, you should write automated tests.
 Test-Driven development is an approach to development where
tests are written before the code to be tested.
 Scenario testing involves inventing a typical usage scenario and
using this to derive test cases.
 Acceptance testing is a user testing process where the aim is to
decide if the software is good enough to be deployed and used in its
operational environment (usually for custom software).

Ian Sommerville, Software Engineering, 9th EditionCh 8

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