Monday, July 14, 2008

Software Testing

Software testing is the process of checking software, to verify that it satisfies its requirements and to detect errors.

Software testing is an empirical investigation conducted to provide stakeholders with information about the quality of the product or service under test, with respect to the context in which it is intended to operate. This includes, but is not limited to, the process of executing a program or application with the intent of finding software bugs.

Quality is not an absolute; it is value to some person. With that in mind, testing can never completely establish the correctness of arbitrary computer software; testing furnishes a criticism or comparison that compares the state and behaviour of the product against a specification. An important point is that software testing should be distinguished from the separate discipline of Software Quality Assurance (S.Q.A.), which encompasses all business process areas, not just testing.

Over its existence, computer software has continued to grow in complexity and size. Every software product has a target audience. For example, the audience for video game software is completely different from banking software. Therefore, when an organization develops or otherwise invests in a software product, it presumably must assess whether the software product will be acceptable to its end users, its target audience, its purchasers, and other stakeholders. Software testing is the process of attempting to make this assessment.

A study conducted by NIST in 2002 reports that software bugs cost the U.S. economy $59.5 billion annually. More than a third of this cost could be avoided if better software testing was performed.

A primary purpose for testing is to detect software failures so that defects may be uncovered and corrected. This is a non-trivial pursuit. Testing cannot establish that a product functions properly under all conditions but can only establish that it does not function properly under specific conditions.] The scope of software testing often includes examination of code as well as execution of that code in various environments and conditions as well as examining the quality aspects of code: does it do what it is supposed to do and do what it needs to do. In the current culture of software development, a testing organization may be separate from the development team. There are various roles for testing team members. Information derived from software testing may be used to correct the process by which software is developed.

Defects and failures
The software faults occur through the following process. A programmer makes an error (mistake), which results in a defect (fault, bug) in the software source code. If this defect is executed, in certain situations the system will produce wrong results, causing a failure.] Not all defects will necessarily result in failures. For example, defects in dead code will never result in failures. A defect can turn into a failure when the environment is changed. Examples of these changes in environment include the software being run on a new hardware platform, alterations in source data or interacting with different software.] A single defect may result in a wide range of failure symptoms.

Input combinations and preconditions
A problem with software testing is that testing under all combinations of inputs and preconditions (initial state) is not feasible, even with a simple product.]] This means that the number of defects in a software product can be very large and defects that occur infrequently are difficult to find in testing. More significantly, parafunctional dimensions of quality (how it is supposed to be versus what it is supposed to do) -- for example, usability, scalability, performance, compatibility, reliability -- can be highly subjective; something that constitutes sufficient value to one person may be intolerable to another.

Static vs. dynamic testing
There are many approaches to software testing. Reviews, walkthroughs or inspections are considered as static testing, whereas actually executing programmed code with a given set of test cases is referred to as dynamic testing.

Software verification and validation
Software testing is used in association with verification and validation:]

Verification: Have we built the software right (i.e., does it match the specification)?
Validation: Have we built the right software (i.e., is this what the customer wants)?

The software testing team
Software testing can be done by software testers. Until the 1950s the term "software tester" was used generally, but later it was also seen as a separate profession. Regarding the periods and the different goals in software testing] there have been established different roles: test lead/manager, test designer, tester, test automater/automation developer, and test administrator.

Software Quality Assurance (SQA)
Thought controversial], software testing may be viewed as an important part of the software quality assurance (SQA) process.[citation needed] In SQA, software process specialists and auditors take a broader view on software and its development. They examine and change the software engineering process itself to reduce the amount of faults that end up in defect rate. What constitutes an acceptable defect rate depends on the nature of the software. An arcade video game designed to simulate flying an airplane would presumably have a much higher tolerance for defects than mission critical software such as that used to control the functions of an airliner. Although there are close links with SQA, testing departments often exist independently, and there may be no SQA function in some companies.

The separation of debugging from testing was initially introduced by Glenford J. Myers in 1979.[8] Although his attention was on breakage testing, it illustrated the desire of the software engineering community to separate fundamental development activities, such as debugging, from that of verification. Dr. Dave Gelperin and Dr. William C. Hetzel classified in 1988 the phases and goals in software testing in the following stages:[9]

Until 1956 - Debugging oriented0]
1957-1978 - Demonstration oriented
1979-1982 - Destruction oriented
1983-1987 - Evaluation oriented
1988-2000 - Prevention oriented

Testing methods
Software testing methods are traditionally divided into black box testing and white box testing. These two approaches are used to describe the point of view that a test engineer takes when designing test cases.

Black box testing
Black box testing treats the software as a black-box without any understanding of internal behavior. It aims to test the functionality according to the requirements. Thus, the tester inputs data and only sees the output from the test object. This level of testing usually requires thorough test cases to be provided to the tester who then can simply verify that for a given input, the output value (or behavior), is the same as the expected value specified in the test case. Black box testing methods include: equivalence partitioning, boundary value analysis, all-pairs testing, fuzz testing, model-based testing, traceability matrix etc.

White box testing
White box testing, however, is when the tester has access to the internal data structures, code, and algorithms.

Types of white box testing
The following types of white box testing exist:

code coverage - creating tests to satisfy some criteria of code coverage. For example, the test designer can create tests to cause all statements in the program to be executed at least once.
mutation testing methods.
fault injection methods.
static testing - White box testing includes all static testing.

Code completeness evaluation
White box testing methods can also be used to evaluate the completeness of a test suite that was created with black box testing methods. This allows the software team to examine parts of a system that are rarely tested and ensures that the most important function points have been tested.

Two common forms of code coverage are:

function coverage, which reports on functions executed
and statement coverage, which reports on the number of lines executed to complete the test.
They both return a coverage metric, measured as a percentage.

Grey Box Testing
In recent years the term grey box testing has come into common usage. This involves having access to internal data structures and algorithms for purposes of designing the test cases, but testing at the user, or black-box level.

Manipulating input data and formatting output do not qualify as grey-box because the input and output are clearly outside of the black-box we are calling the software under test. This is particularly important when conducting integration testing between two modules of code written by two different developers, where only the interfaces are exposed for test. Grey box testing may also include reverse engineering to determine, for instance, boundary values.

Non Functional Software Testing
Special methods exist to test non-functional aspects of software.

Performance testing checks to see if the software can handle large quantities of data or users.
Usability testing is needed to check if the user interface is easy to use and understand.
Security testing is essential for software which processes confidential data and to prevent system intrusion by hackers.
internationalization and localization is needed to test these aspects of software, for which a pseudolocalization method can be used.

Testing process
A common practice of software testing is performed by an independent group of testers after the functionality is developed before it is shipped to the customer. This practice often results in the testing phase being used as project buffer to compensate for project delays, thereby compromising the time devoted to testing.8] Another practice is to start software testing at the same moment the project starts and it is a continuous process until the project finishes.9]

In counterpoint, some emerging software disciplines such as extreme programming and the agile software development movement, adhere to a "test-driven software development" model. In this process unit tests are written first, by the software engineers (often with pair programming in the extreme programming methodology). Of course these tests fail initially; as they are expected to. Then as code is written it passes incrementally larger portions of the test suites. The test suites are continuously updated as new failure conditions and corner cases are discovered, and they are integrated with any regression tests that are developed. Unit tests are maintained along with the rest of the software source code and generally integrated into the build process (with inherently interactive tests being relegated to a partially manual build acceptance process).

Testing can be done on the following levels:

Unit testing tests the minimal software component, or module. Each unit (basic component) of the software is tested to verify that the detailed design for the unit has been correctly implemented. In an object-oriented environment, this is usually at the class level, and the minimal unit tests include the constructors and destructors.0]
Integration testing exposes defects in the interfaces and interaction between integrated components (modules). Progressively larger groups of tested software components corresponding to elements of the architectural design are integrated and tested until the software works as a system.
System testing tests a completely integrated system to verify that it meets its requirements.
System integration testing verifies that a system is integrated to any external or third party systems defined in the system requirements.[citation needed]
Before shipping the final version of software, alpha and beta testing are often done additionally:

Alpha testing is simulated or actual operational testing by potential users/customers or an independent test team at the developers' site. Alpha testing is often employed for off-the-shelf software as a form of internal acceptance testing, before the software goes to beta testing.[citation needed]
Beta testing comes after alpha testing. Versions of the software, known as beta versions, are released to a limited audience outside of the programming team. The software is released to groups of people so that further testing can ensure the product has few faults or bugs. Sometimes, beta versions are made available to the open public to increase the feedback field to a maximal number of future users.[citation needed]
Finally, acceptance testing can be conducted by the end-user, customer, or client to validate whether or not to accept the product. Acceptance testing may be performed as part of the hand-off process between any two phases of development.[citation needed]

Regression testing
Main article: Regression testing
After modifying software, either for a change in functionality or to fix defects, a regression test re-runs previously passing tests on the modified software to ensure that the modifications haven't unintentionally caused a regression of previous functionality. Regression testing can be performed at any or all of the above test levels. These regression tests are often automated.

More specific forms of regression testing are known as sanity testing, when quickly checking for bizarre behaviour, and smoke testing when testing for basic functionality.

Finding faults early
It is commonly believed that the earlier a defect is found the cheaper it is to fix it. The following table shows the cost of fixing the defect depending on the stage it was found. For example, if a problem in requirements is found only post-release, then it would cost 10-100 times more to fix it comparing to the cost if the same fault was already found by the requirements review.

Time Introduced Time Detected
Requirements Architecture Construction System Test Post-Release
Requirements 1 3 5-10 10 10-100
Architecture - 1 10 15 25-100
Construction - - 1 10 10-25

Measuring software testing
Usually, quality is constrained to such topics as correctness, completeness, security,[citation needed] but can also include more technical requirements as described under the ISO standard ISO 9126, such as capability, reliability, efficiency, portability, maintainability, compatibility, and usability.

There are a number of common software measures, often called "metrics", which are used to measure the state of the software or the adequacy of the testing.

Test case
A test case is a software testing document, which consists of event, action, input, output, expected result, and actual result. Clinically defined a test case is an input and an expected result. This can be as pragmatic as 'for condition x your derived result is y', whereas other test cases described in more detail the input scenario and what results might be expected. It can occasionally be a series of steps (but often steps are contained in a separate test procedure that can be exercised against multiple test cases, as a matter of economy) but with one expected result or expected outcome. The optional fields are a test case ID, test step or order of execution number, related requirement(s), depth, test category, author, and check boxes for whether the test is automatable and has been automated. Larger test cases may also contain prerequisite states or steps, and descriptions. A test case should also contain a place for the actual result. These steps can be stored in a word processor document, spreadsheet, database, or other common repository. In a database system, you may also be able to see past test results and who generated the results and the system configuration used to generate those results. These past results would usually be stored in a separate table.

Test script
The test script is the combination of a test case, test procedure, and test data. Initially the term was derived from the product of work created by automated regression test tools. Today, test scripts can be manual, automated, or a combination of both.

Test suite
The most common term for a collection of test cases is a test suite. The test suite often also contains more detailed instructions or goals for each collection of test cases. It definitely contains a section where the tester identifies the system configuration used during testing. A group of test cases may also contain prerequisite states or steps, and descriptions of the following tests.

Test plan
A test specification is called a test plan. The developers are well aware what test plans will be executed and this information is made available to the developers. This makes the developers more cautious when developing their code. This ensures that the developers code is not passed through any surprise test case or test plans.

Test harness
The software, tools, samples of data input and output, and configurations are all referred to collectively as a test harness.

A sample testing cycle
Although variations exist between organizations, there is a typical cycle for testing:

Requirements analysis: Testing should begin in the requirements phase of the software development life cycle. During the design phase, testers work with developers in determining what aspects of a design are testable and with what parameters those tests work.
Test planning: Test strategy, test plan, testbed creation. A lot of activities will be carried out during testing, so that a plan is needed.
Test development: Test procedures, test scenarios, test cases, test scripts to use in testing software.
Test execution: Testers execute the software based on the plans and tests and report any errors found to the development team.
Test reporting: Once testing is completed, testers generate metrics and make final reports on their test effort and whether or not the software tested is ready for release.
Test result analysis: Or Defect Analysis, is done by the development team usually along with the client, in order to decide what defects should be treated, fixed, rejected (i.e. found software working properly) or deferred to be dealt with at a later time.
Retesting the resolved defects. Once a defect has been dealt with by the development team, it is retested by the testing team.
Regression testing: It is common to have a small test program built of a subset of tests, for each integration of new, modified or fixed software, in order to ensure that the latest delivery has not ruined anything, and that the software product as a whole is still working correctly.

Main article: Software testing controversies
Some of the major controversies include:

What constitutes responsible software testing? - Members of the "context-driven" school of testing believe that there are no "best practices" of testing, but rather that testing is a set of skills that allow the tester to select or invent testing practices to suit each unique situation. 8]
Agile vs. traditional - Should testers learn to work under conditions of uncertainty and constant change or should they aim at process "maturity"? The agile testing movement has received growing popularity since 2006 mainly in commercial circles 9], whereas government and military software providers are slow to embrace this methodology, and mostly still hold to CMM.0]
Exploratory vs. scripted - Should tests be designed at the same time as they are executed or should they be designed beforehand?
Manual vs. automated - Some writers believe that test automation is so expensive relative to its value that it should be used sparingly. Others, such as advocates of agile development, recommend automating 100% of all tests.
Software design vs. software implementation - Should testing be carried out only at the end or throughout the whole process?
Who watches the watchmen? - The idea is that any form of observation is also an interaction, that the act of testing can also affect that which is being tested.

Several certification programs exist to support the professional aspirations of software testers and quality assurance specialists. No certification currently offered actually requires the applicant to demonstrate the ability to test software. No certification is based on a widely accepted body of knowledge. This has led some to declare that the testing field is not ready for certification. Certification itself cannot measure an individual's productivity, their skill, or practical knowledge, and cannot guarantee their competence, or professionalism as a tester.

Software testing certification types
Certifications can be grouped into: exam-based and education-based.

Exam-based certifications: For these there is the need to pass an exam, which can also be learned by self-study: e.g. for ISTQB or QAI.
Education-based certifications: Education based software testing certifications are instructor-led sessions, where each course has to be passed, e.g. IIST (International Institute for Software Testing).

Testing certifications
Certified Software Tester (CSTE) offered by the Quality Assurance Institute (QAI)
Certified Software Test Professional (CSTP) offered by the International Institute for Software Testing8]
[[CSTP (TM)]] (Australian Version) offered by K. J. Ross & Associates9]
CATe offered by the International Institute for Software Testing0]
ISEB offered by the Information Systems Examinations Board
Certified Tester, Foundation Level (CTFL) offered by the International Software Testing Qualification Board
Certified Tester, Advanced Level (CTAL) offered by the International Software Testing Qualification Board
CBTS offered by the Brazilian Certification of Software Testing (ALATS)

Quality assurance certifications
CSQE offered by the American Society for Quality (ASQ)
CSQA offered by the Quality Assurance Institute (QAI)

See also
Dynamic program analysis
Formal verification
Reverse Semantic Traceability
Static code analysis
GUI software testing
Web testing


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