Black box testing or functional testing is a method which is used to examine software functionality without knowing its internal code structure. It can be applied to all software testing levels but is mostly employed for the higher level acceptance and system related ones.
To elaborate, a professional using this method to test an application’s functionality will only know about the input and expected output but not about the program which helps the application reach the desired output. The professional will only enter valid and invalid inputs and determine the expected outputs without having any in-depth knowledge of the internal structure.
Black Box Testing Techniques
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Test cases in the black box testing method are built around the specifications, requirements, and design parameters of a software. Some reliable techniques applied to create those test cases are:
Boundary Value Analysis:
The most commonly used black box testing technique, Boundary Value Analysis or BVA is used to find the error in the boundaries of input values rather than the center.
Equivalence Class Partitioning:
This technique is used to reduce the number of possible inputs to small yet effective inputs. Used to test an application exhaustively and avoid redundancy of inputs, it is done by dividing inputs into classes and getting value from each class.
Decision Table Based Testing:
This approach is the most rigorous one and is ideally implemented when the number of combinations of actions is taken under varying conditions.
Cause-Effect Graphing Technique:
This technique considers a system’s desired external behavior only. It helps in selecting test cases which relate Causes to Effects to create test cases. In the aforementioned statement, Cause implies a distinct input condition which results in internal change in a system while Effect implies an output condition brought by a combination of causes.
The success of this technique is solely dependent on the experience of the tester. There are no tools and techniques as such, but one can write test cases either while reading the document or while encountering an undocumented error during the testing.
Advantages / Pros of Black Box Testing
- Unbiased tests because the designer and tester work independently
- Tester is free from any pressure of knowledge of specific programming languages to test the reliability and functionality of an application / software
- Facilitates identification of contradictions and vagueness in functional specifications
- Test is performed from a user’s point-of-view and not of the designer’s
- Test cases can be designed immediately after the completion of specifications
Disadvantages / Cons of Black Box Testing
- Tests can be redundant if already run by the software designer
- Test cases are extremely difficult to be designed without clear and concise specifications
- Testing every possible input stream is not possible because it is time-consuming and this would eventually leave many program paths untested
- Results might be overestimated at times
- Cannot be used for testing complex segments of code
Even though black box testing does not test a system comprehensively, still, it can help one achieve a user’s expectation from an application / software.