Gray-box testing (International English spelling: grey-box testing) is a combination of white-box testing and black-box testing. The aim of this testing is to search for the defects, if any, due to improper structure or improper usage of applications.^[1][2]

A black-box tester is unaware of the internal structure of the application to be tested, while a white-box tester has access to the internal structure of the application. A gray-box tester partially knows the internal structure, which includes access to the documentation of internal data structures as well as the algorithms used.^[3]

Gray-box testers require both high-level and detailed documents describing the application, which they collect in order to define test cases.^[4]

Gray-box testing is beneficial because it takes the straightforward technique of black-box testing and combines it with the code-targeted systems in white-box testing.

Gray-box testing is based on requirement test case generation because it presents all the conditions before the program is tested by using the assertion method. A requirement specification language is used to make it easy to understand the requirements and verify its correctness.^[5]

Object-oriented software consists primarily of objects; where objects are single indivisible units having executable code and/or data. Some assumptions are stated below which are needed for the application of use gray-box testing.

• Activation of Methods^[6]
• State Reporting in Class Under Test (CUT).
• Report Testing is inherent in Class Under Test.^[5]

• Architectural model
• Unified Modeling Language - UML Design Model
• Finite-state machine - State Model.^[7][8]

Cem Kaner defines "gray-box testing as involving inputs and outputs, but test design is educated by information about the code or the program operation of a kind that would normally be out of view of the tester".^[9] Gray-box testing techniques are:

• Matrix Testing: states the status report of the project.
• Regression testing: it implies rerunning of the test cases if new changes are made.
• Pattern Testing: verify the good application for its design or architecture and patterns.
• Orthogonal array testing: used as subset of all possible combination.^[10]

• Gray-box testing is well suited for web applications. Web applications have distributed network or systems; due to absence of source code or binaries it is not possible to use white-box testing. Black-box testing is also not used due to just contract between customer and developer, so it is more efficient to use gray-box testing as significant information is available in Web Services Description Language (WSDL).^[13]
• Gray-box testing is suited for functional or business domain testing. Functional testing is done basically a test of user interactions with may be external systems. Gray-box testing is well-suited for functional testing due to its characteristics; it also helps to confirm that software meets the requirements defined for the software.^{[14][15][16][17]}

The distributed nature of Web services allows gray-box testing to detect defects within a service-oriented architecture (SOA). As we know, white-box testing is not suitable for Web services as it deals directly with the internal structures. White-box testing can be used for state art methods; for example, message mutation which generates the automatic tests for large arrays to help exception handling states, flow without source code or binaries. Such a strategy is useful to push gray-box testing nearer to the outcomes of white-box testing.

• Grey box model