Gray Box Testing in Software Development

Gray Box Testing is a technique to test the software product or application with partial knowledge of the internal workings of an application.

In this process, context-specific errors that are related to web systems are commonly identified. It will increase the testing coverage by concentrating on all of the layers of any complex system.

Gray Box Testing is a software testing method, which is a combination of both White Box Testing and Black Box Testing method.

  • In White Box testing internal structure (code) is known
  • In Black Box testing internal structure (code) is unknown
  • In Grey Box Testing internal structure (code) is partially known

Gray Box Testing gives the ability to test both sides of an application, presentation layer as well as the code part. It is primarily useful in Integration Testing and Penetration Testing.

Example of Gray Box Testing:

While testing websites feature like links or orphan links, if tester encounters any problem with these links, then he can make the changes straightaway in HTML code and can check in real time.

Gray Box Testing Strategy

To perform Gray box testing, it is not necessary that the tester has access to the source code. Tests are designed based on the knowledge of algorithm, architectures, internal states, or other high-level descriptions of the program behavior.
To perform Gray box Testing-

  • It applies a straight forward technique of black box testing
  • It is based on requirement test case generation; as such it presets all the conditions before the program is tested by the assertion method.

Techniques used for Grey box Testing are-

  • Matrix Testing: This testing technique involves defining all the variables that exist in their programs.
  • Regression Testing: To check whether the change in the previous version has regressed other aspects of the program in the new version. It will be done by testing strategies like retest all, retest risky use cases, retest within a firewall.
  • Orthogonal Array Testing or OAT: It provides maximum code coverage with minimum test cases.
  • Pattern Testing: This testing is performed on the historical data of the previous system defects. Unlike black box testing, gray box testing digs within the code and determines why the failure happened

Usually, Grey box methodology uses automated software testing tools to conduct the testing. Stubs and module drivers are created to relieve tester to manually generate the code.

Steps to perform Grey box Testing are:

  1. Identify inputs
  2. Identify outputs
  3. Identify major paths
  4. Identify Subfunctions
  5. Develop inputs for Subfunctions
  6. Develop outputs for Subfunctions
  7. Execute test case for Subfunctions
  8. Verify correct result for Subfunctions
  9. Repeat steps 4 & 8 for other Subfunctions
  10. Repeat steps 7 & 8 for other Subfunctions

The test cases for grey box testing may include, GUI related, Security related, Database related, Browser related, Operational system related, etc.

Gray Box Testing Challenges

  • When a component under test encounter a failure of some kind may lead to abortion of the ongoing operation
  • When test executes in full but the content of the result is incorrect.


  • The overall cost of system defects can be reduced and prevented from passing further with Grey box testing
  • Grey box testing is suited more for GUI, Functional Testing, security assessment, web applications, web-services, etc.
  • Techniques used for Grey box Testing
    • Matrix Testing
    • Regression Testing
    • OAT or Orthogonal Array Testing
    • Pattern Testing

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