Testing Methods

Approach of boxes
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 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 of software according to the applicable requirements. Thus, the tester inputs data into, 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), either "is" or "is not" the same as the expected value specified in the test case.
Specification-based testing is necessary, but it is 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 do not. But, on the other hand, black box testing has been said to be "like a walk in a dark labyrinth without a flashlight," because the tester doesn't know how the software being tested was actually constructed. As a result, there are situations when
(1) a tester writes many test cases to check something that could have been 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 is when the tester has access to the internal data structures and algorithms including the code that implement these.
Types of white box testing
The following types of white box testing exist:

API testing (application programming interface) - Testing of the application using Public and Private APIs
Code coverage - creating tests to satisfy some criteria of code coverage (e.g., the test designer can create tests to cause all statements in the program to be executed at least once)
Fault injection methods
Mutation testing 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
Statement coverage, which reports on the number of lines executed to complete the test
They both return a code coverage metric, measured as a percentage.


Grey box testing 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" that we are calling the system under test. This distinction 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. However, modifying a data repository does qualify as grey box, as the user would not normally be able to change the data outside of the system under test. Grey box testing may also include reverse engineering to determine, for instance, boundary values or error messages.

Main article: Integration testing
Integration testing is any type of software testing, that seeks to uncover collisions of individual software modules to each other. Such integration defects can arise, when the new modules are developed in separate branches, and then integrated into the main project.

Main article: Regression testing
Regression testing is any type of software testing, that seeks to uncover software regressions. Such regression occur whenever software functionality, that was previously working correctly, stops working as intended. Typically, regressions occur as an unintended consequence of program changes, when the newly developed part of the software collides with the previously existing. Common methods of regression testing include re-running previously run tests and checking whether previously fixed faults have re-emerged. The depth of testing depends on the phase in the release process and the risk of the added features. They can either be complete, for changes added late in the release or deemed to be risky, to very shallow, consisting of positive tests on each feature, if the changes are early in the release or deemed to be of low risk.

Main article: Acceptance testing
Acceptance testing can mean one of two things:
A smoke test is used as an acceptance test prior to introducing a new build to the main testing process, i.e. before integration or regression.
Acceptance testing performed by the customer, often in their lab environment on their own HW, is known as user acceptance testing (UAT).

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. This activity of Non Functional Software Testing is often referred to as Endurance Testing.
Stability testing checks to see if the software can continuously function well in or above an acceptable period. This activity of Non Functional Software Testing is oftentimes referred to as load (or endurance) testing.
Usability testing is needed to check if the user interface is easy to use and understand.
Security testing is essential for software that processes confidential data 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..

Main article: Destructive testing
Destructive testing attempts to cause the software or a sub-system to fail, in order to test its robustness.

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.

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 have not 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 (which quickly checks for bizarre behavior) and smoke testing (which tests 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.


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 the requirements is found only post-release, then it would cost 10–100 times more to fix than if it had already been found by the requirements review.