SE2011_10.ppt

Chapter 8 – Software Testing
1
Chapter 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
2

Why do we test software?
… so that the following does not happen:
In 1991, the owner & chief engineer of Sierra Software
Innovations was under pressure to release the code modules he
sold before they were finished.
When I walked in one Monday morning several packages
already shipped (back then we sold code by postal mail). I
thought I would give the code modules a whirl and see what is
being released … The modules did not even compile.
Chapter 8 Software testing 3

Program Testing
DUAL PURPOSE
1. Shows that a program runs as it is intended to do.
2. Helps to discover program defects.
- Reveals the presence of errors NOT their absence.

 Verification:
"Are we building the product right?”
 The software should conform to its specification.
 Validation:
"Are we building the right product?”
 The software should do what the user really requires.
Verification vs validation
5

Engineering Groups
Who does what at a company?
· Validation · Verification · Verification

Stages of Testing
1. Development testing - the system is tested during
development to discover bugs and defects.
2. Release testing – the product test group tests a
complete version of the system before it is released to
users.
3. User testing – potential future users of a system test it in
their own environment. Beta testing.

Stages of Testing
… Development Testing
 Development testing includes all testing activities that
are carried out by the team developing the system.
1. Unit testing, where individual program units or object classes
are tested. Unit testing should focus on testing the functionality
of objects or methods.
2. Component testing, where several individual units are
integrated to create composite components. Component
testing should focus on testing component interfaces.
3. System testing, where some or all of the components in a
system are integrated and the system is tested as a whole.
System testing should focus on testing component interactions.
4. Inspections & reviews – engineer review the code developed
by other engineers.

Stages of Testing
…Development Testing
…… Unit testing
 Unit testing is the process of testing individual
components in isolation.
 It is a defect testing process.
 Units may be:
 Individual functions or methods within an object
 Object classes with several attributes and methods
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Stages of Testing
…… Unit testing
EXAMPLE
1. Implement Math function “Square Root”.
2. Function returns -1 for negative input.
3. Function rounds to nearest integer.
int sqrt_fnc(int number);
Test program:
…
test_sqrt_fnc();
…
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Stages of Testing
…… Unit testing
test_sqrt_fnc()
{
if (sqrt_fnc(0) != 0)
printf(“sqrt_fnc FAILED!n”);
else if (sqrt_fnc(101) != 10)
else if (sqrt_fnc(-100) != -1)
else
printf(“sqrt_fnc PASSED!n”);
}
11

Stages of Testing
……Unit testing
……… Automated testing
 Whenever possible, unit testing should be automated so
that tests are run and checked without manual
intervention.
 In automated unit testing, make use of a test automation
framework (such as JUnit) to write and run your program
tests.
 Unit testing frameworks provide generic test classes that
you extend to create specific test cases. They can then
run all of the tests that you have implemented and
report, often through some GUI, on the success of the
tests.

Stages of Testing
……Unit testing
……… Unit test effectiveness
 The test cases should show that, when used as
expected, the unit that you are testing does what it is
supposed to do.
 If there are defects in the component, these should be
revealed by test cases.
 This leads to 2 types of unit test cases:
 The first of these should reflect normal operation of a program
and should show that the component works as expected.
 The other kind of test case should be based on testing
experience of where common problems arise. It should use
abnormal inputs to check that these are properly processed and
do not crash the component.
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Stages of Testing
……Unit Testing
……… 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.
Object Testing can be very complex and difficult. Why?
 Inheritance makes testing complex and difficult.
 Object oriented programming is complex.
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Stages of Testing
……Unit Testing
……… The weather station object interface
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Stages of Testing
……Unit Testing
……… 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
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Stages of Testing
……Unit Testing
……… Test-driven development
 Test-driven development (TDD) is an approach to
program development in which you inter-leave testing
and code development.
 Tests are written before code and ‘passing’ the tests is
the critical driver of development.
 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.
17

Stages of Testing
……Unit Testing
……… Test-driven development
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Stages of Testing
……Unit Testing
……… TDD process activities
 Start by identifying the increment of functionality that is
required. This should normally be small and
implementable in a few lines of code.
 Write a test for this functionality and implement this as
an automated test.
 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.
 Implement the functionality and re-run the test.
 Once all tests run successfully, you move on to
implementing the next chunk of functionality.
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Stages of Testing
……Unit Testing
……… 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.
 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.
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Stages of Testing
……Unit Testing
……… Regression testing
 Regression testing is testing the system to check that
changes have not ‘broken’ previously working code.
 In a manual testing process, regression testing is
expensive but, with automated testing, it 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.
21

Stages of Testing
…… Component testing
 Software components are often composite components
that are made up of several interacting objects.
 For example, in the weather station system, the reconfiguration
component includes objects that deal with each aspect of the
reconfiguration.
 You access the functionality of these objects through the
defined component interface.
 Testing composite components should therefore focus
on showing that the component interface behaves
according to its specification.
 You can assume that unit tests on the individual objects within
the component have been completed.

Stages of Testing
……Component testing
……… Interface testing
 Objectives are to detect faults due to interface errors or
invalid assumptions about interfaces.
 Interface types
 Parameter interfaces Data passed from one method or
procedure to another.
 Shared memory interfaces Block of memory is shared between
procedures or functions.
 Procedural interfaces Sub-system encapsulates a set of
procedures to be called by other sub-systems.
 Message passing interfaces Sub-systems request services from
other sub-systems
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Stages of 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.
 Interface misunderstanding
 A calling component embeds assumptions about the behaviour
of the called component which are incorrect.
 Timing errors
 The called and the calling component operate at different speeds
and out-of-date information is accessed.
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Stages of Testing
……… 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.
25

Stages of Testing
…… System testing
 System testing during development involves integrating
components to create a version of the system and then
testing the integrated system.
 The focus in system testing is testing the interactions
between components.
 System testing checks that components are compatible,
interact correctly and transfer the right data at the right
time across their interfaces.
 System testing tests the emergent behaviour of a
system.
26

Stages of Testing
…… System and component testing
 During system testing, 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.

 Software inspections Concerned with analysis of
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 Concerned with exercising and
observing product behaviour (dynamic verification)
 The system is executed with test data and its operational
behaviour is observed.
Stages of Testing
…… Inspections and testing
28

Stages of Testing
…… Software Inspections
 These involve people examining the source
representation with the aim of discovering anomalies and
defects.
 Inspections do not require execution of a system so may
be used before implementation.
 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.
29

Stages of Testing
…… Software Inspections
BUT – not in the book
 Inspections also involve engineers looking through the
source code developed by other engineers.
 Companies that have ISO 9000 certification in product
development are required to have engineering reviews of
source code.
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Stages of Testing
……Software Inspections
……… 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.

Stages of Testing
……Software Inspections
……… Inspections and testing
 Inspections and testing are complementary and not
opposing verification techniques.
 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.
32

Stages of Testing
…… Program testing goals
 To demonstrate to the developer and the customer that
the software meets its requirements.
 For custom software, this means that there should be at least
one test for every requirement in the requirements document.
 For generic software products, it means that there should be
tests for all of the system features, plus combinations of these
features, that will be incorporated in the product release.
 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.
33

Stages of Testing
…… An input-output model of program testing
34

Stages of Testing
… Test Levels
 Software testing aims to establish confidence that the
system is ‘fit for purpose’.
 How much to test 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.
35

Stages of Testing
…… Testing guidelines (sequences)
 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.
36

Stages of Testing
…… 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.
37

Stages of Testing
…… Use-case 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.

Stages of Testing
…… 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.

Stages of Testing
… Release testing
 Release testing is the process of testing a particular release
of a system that is intended for use outside of the
development team.
 The primary goal of the release testing process is to
convince the supplier of the system that it is good enough
for use.
 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.
 Release testing is usually a black-box testing process
where tests are only derived from the system specification.
40

Stages of Testing
… 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.
41

Stages of Testing
… Requirements based testing
 Requirements-based testing involves examining
each requirement and developing a test or tests
for it.
42

Stages of Testing
… Performance testing
 Part of release testing may involve testing 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.
43

Stages of Testing
… 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.
44

Stages of Testing
… 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.
45

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, in which you
test individual objects and methods, component testing
in which you test related groups of objects, and system
testing, in which you test partial or complete systems.

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. The tests are
embedded in a program that can be run every time a change is
made to a system.
 Test-first 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.
47

Summary – who does what?
48
Product Design Group Product Development Group Product Test Group
Development Testing
Release Testing
User Testing
Validation
Verification
Product concept
Unit Testing
Component Testing
System Testing
Automated Testing
Regression Testing
Incremental Development
Inspections & Reviews
X
X
X
X X
X
X
X
X
X
X
X
X
X

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