Software testing is the process used to assess the quality of computer software. Software testing is an empirical technical 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, a video game software has its audience 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 §59.5 billions to U.S economy. More than a third of this cost could be avoided if a better software testing would be done.
 

Scope

Software testing may be viewed as an important part of the software quality assurance (SQA) process. 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 software used to control an actual airliner. Although there are close links with SQA testing departments often exist independently, and there may be no SQA areas in some companies.

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 a 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 problem with software testing is that testing all combinations of inputs and preconditions is not feasible when testing anything other than a simple product.^[4] 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--for example, usability, scalability, performance, compatibility, reliability--can be highly subjective; something that constitutes sufficient value to one person may be intolerable to another.

• 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)?

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, tester, test designer, test automater/automation developer, and test administrator.

Testing methods

Black box testing treats the software as a black-box without any understanding as to how the internals behave. 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 behaviour), 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 etc.

White box testing, however, is when the tester has access to the internal data structures, code, and algorithms. White box testing methods include creating of tests to satisfy some code coverage criteria. For example, the test designer can create tests to make all statement in the program to be executed at least once. Other examples of white box testing are mutation testing and fault injection methods.

White box testing methods can be also used to evaluate the completness of test suite, which 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 percentag

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.

Testing process

A common practice of software testing is that it is performed by an independent group of testers after the functionality is developed but 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).

Pre-release testing

• 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.
  
• Functional testing tests at any level (class, module, interface, or system) for proper functionality as defined in the specification. The use of a traceability matrix often helps with functional testing.
  
• 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.
  
• Performance testing validates whether the quality of service (sometimes called non-functional requirements) parameters defined at the requirements stage is met by the final product.
  
• 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.
  

Post release testing

• 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.

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.

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.

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:

• Bugs found per tester per unit time (day/week/month).
• Total bugs found in a release.
• Total bugs found in a module or feature.
• Bugs found or fixed per build.
• Number of customer reported bugs (as a measure of testing effectiveness).
• Bug trend over the period in a release. (Bugs should converge towards zero as the project gets closer to release. It is possible that there are more cosmetic bugs found closer to release - in which case the number of critical bugs found is used instead of total number of bugs found.)
• Number of test cases executed per person per unit time.
• Percent of test cases executed so far, total pass, total fail.

Testing Artifacts
 

Software testing process can produce several artifacts. 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 tabl

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.

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.

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.

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 testing varies between organizations, there is a cycle to 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.
• Retesting the defects. Not all errors or defects reported must be fixed by a software development team. Some may be caused by errors in configuring the test software to match the development or production environment. Some defects can be handled by a workaround in the production environment. Others might be deferred to future releases of the software, or the deficiency might be accepted by the business user. There are yet other defects that may be rejected by the development team (of course, with due reason) if they deem it.