Black Box Testing

• Application is treated as a BB where internal mechanism is unknown.
• The process of giving the input to the system and checking the output of the system, without knowing about how the system generates the output is called “BBT”.       

• " BBT " symbolizes not being able to see the inner workings of the software so that only the end-user experience can be tested.
• Black-box is based on requirements and functionality, not code.
• Also called as Behavioral and Specification Based Testing.
• Generally done by software testers.

Why not by developers? 

• Very difficult to break one’s own codexperience 
• To test the software from end-user perspective 

Levels Applicable To Black Box Testing method is applicable to the following levels of software testing:

1. Integration Testing
2. System Testing
3. Acceptance Testing

Definition by ISTQB:

black box testing: Testing, either functional or non-functional, without reference to the internal structure of the component or system.

black box test design technique: Procedure to derive and/or select test cases based on an analysis of the specification, either functional or non-functional, of a component or system without reference to its internal structure.

EXAMPLES :

• Best example of BBT is search on Google . Users just enters keywords and gets expected results in turn.

• Another Example of BBT is Calculator

  BBT Techniques: 

• Equivalence Partitioning 
• Boundary-Value Analysis
• Decision Tables
• State Transition Diagrams
• Error Guessing

Advantages:

• Entire testing is based only on specifications i.e. what the software is expected to do. Hence, it replicates ‘users’ outlook of application use.
• Tests can be created as soon as the functional specifications are base lined.
• Tester can be non-technical.

There is no need for the tester to have detailed functional knowledge of system.

Disadvantages:

• It does not identify the location of the defect and the reason of failure.
• There is a high probability of repeating tests already performed by the programmer.
• Code related issues cannot be traced with BBT like
• Memory allocated not made free after use 
• Variables declared but not used
• Some functions never getting called or unreachable code
• Test cases are challenging to design without having clear functional specifications.

Ref.