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  Date: 14^th May 2010

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Software Testing

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. Testing can never completely establish the correctness of computer software. Instead, it furnishes a criticism or comparison that compares the state and behaviour of the product against oracles—principles or mechanisms by which someone might recognize a problem.

These oracles may include (but are not limited to) specifications, comparable products, past versions of the same product, inferences about intended or expected purpose, user or customer expectations, relevant standards, applicable laws, or other criteria.

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

Scope

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

Not all software defects are caused by coding errors. One common source of expensive defects is caused by requirements gaps, e.g., unrecognized requirements, that result in errors of omission by the program designer. A common source of requirements gaps is non-functional requirements such as testability, maintainability, usability, performance, and security.

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.

Compatibility

A frequent cause of software failure is compatibility with another application or new operating system (or, increasingly web browser version). In the case of lack of backward compatibility this can occur because the programmers have only considered coding the programs for, or testing the software, on the latest operating system they has access to or else, in isolation (no other conflicting applications running at the same time) or under 'ideal' conditions ('unlimited' memory; 'superfast' processor; latest operating system incorporating all updates, etc). In effect, everything is running "as intended" but not when executing at the same time on the same machine with the particular combination of software and/or hardware.

These are some of the hardest failures to predict, detect and test for and many are therefore discovered only after release into the larger world with its largely unknown mix of applications, software and hardware.

It is likely that an experienced programmer will have had exposure to these factors through "co-evolution" with several older systems and be much more aware of potential future compatibility problems and therefore tend to use tried and tested functions or instructions rather than always the latest available which may not be fully compatible with earlier mixtures of software/hardware. This could be considered a prevention oriented strategy that fits well with the latest testing phase suggested by Dr. Dave Gelperin and Dr. William C. Hetzel cited below

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, non-functional 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. The former can, and unfortunately in practise often is, omitted, whereas the latter takes place when programs begin to be used for the first time - which is normally considered the beginning of the testing stage.

This may actually begin before the program is 100% complete in order to test particular sections of code (modules or discrete functions). For example, Spreadsheet programs are, by their very nature, tested to a large extent "on the fly" during the build process as the result of some calculation or text manipulation is shown interactively immediately after each formula is entered.

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)?. It's process based.

Validation: Have we built the right software (i.e., is this what the customer wants)?. It's product based.

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[8] there have been established different roles: test lead/manager, test designer, tester, test automater/automation developer, and test administrator.

Software Quality Assurance (SQA)

Though 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.

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 knowledge of internal implementation. Black box testing methods include: equivalence partitioning, boundary value analysis, all-pairs testing, fuzz testing, model-based testing, traceability matrix, exploratory testing, specification based testing, etc.

Specification Based Testing

Specification Based Testing 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.

Specification based testing is necessary but insufficient to guard against certain risks.

White box testing

White box testing, by contrast to black box testing, is when the tester has access to the internal data structures and algorithms (and the code that implement these)

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 or error messages.

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. This is generally referred to as software scalability.

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 Another practice is to start software testing at the same moment the project starts and it is a continuous process until the project finishes

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.

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

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

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

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.

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.

Benchmarks may be employed during regression testing to ensure that the performance of the newly modified software will be at least as acceptable as the earlier version or, in the case of code optimization, that some real improvement has been achieved.

Source : Software Testing Website.

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