Black Box Testing in Software Engineering

black box testing

What is Black Box Testing?

Black box testing is also defined as a testing technique in which the functionality of the Application Under Test (AUT) is tested without looking for the internal code structure, implementation details and other knowledge of internal paths of the software. This type of testing is based entirely on the software requirements and other specifications.

In this kind of Testing we have to just focus on inputs and the output of the software system without bothering about any internal knowledge of the software program.

The above Black-Box can also be any software system that you want to test. For an Example, an operating system ( OS ) like the Windows, a website like Google or a database like the Oracle or can even be your own custom application. Under this kind of Testing, you can mainly test these applications by just keep focusing on the inputs and outputs without knowing any of their internal code implementation.

How to Perform this Testing

Here are some most basic steps that must be followed to carry out any type of Black Box Testing.

  • Initially, all the requirements and specifications of required system are examined.
  • Tester chooses the valid inputs (positive test scenario) to check whether the SUT processes them correctly or not. Also, some of the invalid inputs (negative test scenario) are also chosen to verify that SUT is able to detect them.
  • Tester also determines the expected outputs for all those inputs.
  • Software tester mainly constructs test cases with all the selected inputs.
  • The test cases are then executed.
  • Software tester also compares the actual outputs with the outputs that was expected.
  • If any kind of defects are found it is fixed and re-tested.

Types of Black Box Testing

There are mainly several types of Black Box Testing but the following three are the most prominent ones –

  • Functional testing – This black box testing type is basically related to the functional requirements of a system; it is done by the software testers.
  • Non-functional testing – This type of testing is not related to any kind of testing related to specific functionality, but the non-functional requirements such as the usability, performance and scalability.
  • Regression testing – Regression Testing is done just after code fixes, upgrades or any other kind of system maintenance for checking the new code whether it has affected the existing code.

Tools used for this Testing:

Tools that are used for Black box testing mainly depends on the type of black box test that you are doing.

  • For the Functional/ Regression Tests you can use either QTP or Selenium. 
  • For the Non-Functional Tests, you can use either Jmeter or LoadRunner.

Black Box Testing Techniques

Following are the most prominent test strategies amongst the many that are used in Black box Testing

  • Equivalence Class Testing: It is used to reduce the total number of possible test cases to an desirable level while maintaining the reasonable test coverage.
  • Boundary Value Testing: The Boundary value testing is mainly focused on the values at the boundaries. This technique is used to determine whether any certain range of values entered are acceptable by the system or not. It is very useful in minimizing the number of test cases. It is most suitable for those systems where an input is within the certain ranges.
  • Decision Table Testing: A decision table puts all the caus9es and their effects in a matrix system. There is a unique combination in every column.

Comparison of Black Box and the White Box Testing:

Black Box Testing

White Box Testing

The primary focus of this testing is on the validation of your functional requirements.

White box testing (Unit Testing) validates the internal structure and the working of your software code

Black box testing gives the abstraction from the code and keep its focus on testing effort of the software system behavior.

To conduct the White Box Testing, Basic knowledge of underlying programming language is very essential. Every Current day software systems use various kind of programming languages and the technologies and it is not possible to know all of them.

Black box facilitates the testing communication amongst modules

White box testing does not facilitate the testing communication amongst modules

Black Box and the Software Development Life Cycle (SDLC)

The Black box uses its own life cycle that is named as Software Testing Life Cycle (STLC) and it is also relative to every stage of the Software Development Life Cycle in Software Engineering.

  • Requirement – This is the First/Initial stage of SDLC and in this stage, the entire requirement is gathered. Software testers also takes part in the requirement stage.
  • Test Planning & Analysis – Testing Types that is applicable to the project are determined. A Test Plan is also created which is used to determine all the possible project risks and their mitigation.
  • Design – In this stage all the Test cases/scripts are created on the basis of the software requirement documents
  • Test Execution– In this final stage the Test Cases prepared are now executed. Bugs if any are fixed in this process and then re-tested.


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