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.

Overview

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.

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 and specification-based testing.

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.

Advantages and disadvantages

The black box tester has no "bonds" with the code, and a tester's perception is very simple: A code must have bugs. Using the principle, "Ask and you shall receive", black box testers find bugs where programmers don't. but, on the other hand, black box testing is like a walk in a dark labyrinth without a flashlight, because the tester doesn't know how the back end was actually constructed. That's why there are situations when 1. A black box tester writes many test cases to check something that can be tested by only one test case and/or 2. Some parts of the back end are not tested at all.

Therefore, black box testing has the advantage of an unaffiliated opinion on the one hand and the disadvantage of blind exploring on the other.

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

• 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.

• Function coverage, which reports on functions executed.
• 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.

In contrast to functional testing, which establishes the correct operation of the software (correct in that it matches the expected behavior defined in the design requirements), non-functional testing verifies that the software functions properly even when it receives invalid or unexpected inputs. Software fault injection, in the form of fuzzing is an example of non-functional testing. Non-functional testing, especially for software, is designed to establish whether the device under test can tolerate invalid or unexpected inputs, thereby establishing the robustness of input validation routines as well as error-handling routines. Various commercial non-functional testing tools are linked from the software fault injection page; there are also numerous open-source and free software tools available that perform non-functional testing.