Conceitos básicos de teste de software

1Teste e Qualidade de Software, MEI/ProDEI/MIEIC/LEIC, João Pascoal Faria, 2006

TQS - Teste e Qualidade de Software

(Software Testing and Quality)

Software Testing Concepts

João Pascoal Faria

[email protected] www.fe.up.pt/~jpf


Software testing

Software testing consists of the dynamic (1) verification of the behavior of a program on a finite (2) set of test cases, suitably selected (3) from the usually infinite executions domain, against the specified expected (4) behavior [source: SWEBOK]

• (1) testing always implies executing the program on some inputs • (2) for even simple programs, too many test cases are

theoretically possible that exhaustive testing is infeasible - trade-off between limited resources and schedules and inherently

unlimited test requirements• (3) see test case design techniques later on how to select the test

cases• (4) it must be possible to decide whether the observed outcomes

of the program are acceptable or not - the pass/fail decision is commonly referred to as the oracle problem


Purpose of software testing

"Program testing can be used to show the presence of bugs, but never to show their absence!” [Dijkstra, 1972] • Because exhaustive testing is usually impossible

"The goal of a software tester is to find bugs, find them as early as possible, and make sure that they get fixed“ (Ron Patton)

A secondary goal is to assess software quality• Defect testing – find defects, using test data and test cases that

have higher probability of finding defects

• Statistical testing – estimate the value of software quality metrics, using representative test cases and test data


Test case - inputs to test the system and the expected outputs (or predicted results) from these inputs if the system operates correctly under specified execution conditions• Inputs may include an initial state of the system

• Outputs may include a final state of the system

• When test cases are executed, the system is provided with the specified inputs and the actual outputs are compared with the outputs expected

Example for a calculator:• 3 + 5 (input) should give 8 (output)

Test cases


Test types

unit

integration

system

performancerobustness

functional behaviour

white box (or

structural)

black box(or

functional)

Level or phase

Accessibility

(test case design strategy/technique)

Quality attributes

usability

reliability

security

focus here


Test levels or phases (1)

Unit testing •Testing of individual program units or

components

•Usually the responsibility of the component developer (except sometimes for critical systems)

•Tests are based on experience, specifications and code

•A principal goal is to detect functional and structural defects in the unit



Integration testing•Testing of groups of components integrated to

create a sub-system

•Usually the responsibility of an independent testing team (except sometimes in small projects)

•Tests are based on a system specification (technical specifications, designs)

•A principal goal is to detect defects that occur on the interfaces of units and their common behavior



System testing•Testing the system as a whole

•Usually the responsibility of an independent testing team

•Tests are usually based on a requirements document (functional requirements/specifications and quality requirements)

•A principal goal is to evaluate attributes such as usability, reliability and performance (assuming unit and integration testing have been performed)

(source: I. Sommerville)



Acceptance testing•Testing the system as a whole•Usually the responsibility of the customer•Tests are based on a requirements specification

or a user manual•A principal goal is to check if the product meets

customer requirements and expectations

Regression testing•Repetition of tests at any level after a software

change(source: I. Sommerville)


Test levels and the extended V-model of software development

Specify Requiremen

ts

Design

Code

Requirements review

Design review

Unit test plan & test cases

review/audit

Execute unit tests

Execute integration

tests

Execute acceptance

tests

System/acceptance test plan & test cases

review/audit

Specify/Design Code Unit tests

Execute system tests

Integration test plan & test cases

review/audit

Specify/Design Code System/acceptance tests

Specify/Design Code Integration tests

Code reviews (source: I. Burnstein,

pg.15)


What is a good test case? Capability to find defects

• Particularly defects with higher risk• Risk = frequency of failure (manifestation to users) * impact of failure • Cost (of post-release failure) ≈ risk

Capability to exercise multiple aspects of the system under test

• Reduces the number of test cases required and the overall cost

Low cost• Development: specify, design, code• Execution• Result analysis: pass/fail analysis, defect localization

Easy to maintain• Reduce whole life-cycle cost• Maintenance cost ≈ size of test artefacts

(See also an article with this title by Cem Kaner)


The importance of good test cases

Product quality

Test

su

ite q

uality

High

Low High

Low

Many bugs found

Very few bugs found

Some bugs found

You may be here …

… and think you are here

Some bugs found


Test selection/adequacy/coverage/stop criteria “A selection criteria can be used for selecting the test cases

or for checking whether or nor a selected test suite is adequate, that is, to decide whether or not the testing can be stopped” [SWEBOK 2004]

Adequacy criteria - Criteria to decide if a given test suite is adequate, i.e., to give us “enough” confidence that “most” of the defects are revealed

• In practice, reduced to coverage criteria

Coverage criteria• Requirements/specification coverage

- At least one test case for each requirement- Cover all statements in a formal specification

• Model coverage- State-transition coverage- Use-case and scenario coverage

• Code coverage - Statement coverage- Data flow coverage, ...

• Fault coverageSoftware Unit Test Coverage and Adequacy, Hong Zhu et al, ACM Computing Surveys, December 1997

“Although it is common in current softwaretesting practice that the test processesat both the higher and lowerlevels stop when money or time runsout, there is a tendency towards the useof systematic testing methods with theapplication of test adequacy criteria.”


Test case design strategies and techniques

Black-box testing(not code-based)

(sometimes called functional testing)

White-box testing(also called code-based

or structural testing)

Outputs

Inputs

Techniques /

Methods

Strategies

Knowledge

sources

Requirements documentSpecificationsUser manualModelsDomain knowledgeDefect analysis dataIntuitionExperience

Equivalence class partitioning Boundary value analysisCause effect graphingError guessingRandom testingState-transition testingScenario-based testing

Program codeControl flow graphsData flow graphsCyclomatic complexityHigh-level designDetailed design

Control flow testing/coverage:- Statement coverage- Branch (or decision) coverage- Condition coverage- Branch and condition coverage- Modified condition/decision coverage- Multiple condition coverage- Independent path coverage- Path coverageData flow testing/coverageClass testing/coverage Mutation testing

Tester's View

(adapted from: I. Burnstein, pg.65)


Test iterations: test to pass and test to fail First test iterations: Test-to-pass

• check if the software fundamentally works • with valid inputs• without stressing the system

Subsequent test iterations: Test-to-fail • try to "break" the system• with valid inputs but at the operational limits• with invalid inputs

(source: Ron Patton)


Test automation

Automatic test case execution• Requires that test cases are written in some executable language• Increases test development costs (coding) but practically

eliminates test (re)execution costs, which is particularly important in regression testing

• Unit testing frameworks and tools for API testing• Capture/replay tools for GUI testing

Automatic test case generation• Automatic generation of test inputs is easier than the automatic

generation of test outputs (usually requires a formal specification) • Reduces test development costs• Usually, inferior capability to find defects per test case, but

overall capability may be higher because much more test cases can be generated (than manually)


Some good practices

Test as early as possible

Write the test cases before the software to be tested• applies to any level: unit, integration or system• helps getting insight into the requirements

Code the test cases• because of the frequent need for regression testing (repetition of testing

each time the software is modified)

The more critical the system the more independent should be the tester

• colleague, other department, other company

Be conscious about cost

Derive expected test outputs from specification (formal/informal, explicit/implicit), not from code


References and further reading

Practical Software Testing, Ilene Burnstein, Springer-Verlag, 2003

Software Testing, Ron Patton, SAMS, 2001

Testing Computer Software, 2nd Edition, Cem Kaner, Jack Falk, Hung Nguyen, John Wiley & Sons, 1999

Guide to the Software Engineering Body of Knowledge (SWEBOK), IEEE Computer Society, http://www.swebok.org/

Software Engineering, Ian Sommerville, 6th Edition, Addison-Wesley, 2000

What Is a Good Test Case?, Cem Kaner, Florida Institute of Tecnology, 2003

Software Unit Test Coverage and Adequacy, Hong Zhu et al, ACM Computing Surveys, December 1997

Conceitos básicos de teste de software

Documents

test levels

system testing

test data

representative test

afinite2set of test

number of test cases

output test cases

software software testing