Black Box Testing
Black Box Testing, also known as Behavioral Testing, is a software testing method in which the internal structure/design/implementation of the item being tested is not known to the tester. These tests can be functional or non-functional, though usually functional.
This method is named so because the software program, in the eyes of the tester, is like a black box; inside which one cannot see.
This method attempts to find errors in the following categories:
- Incorrect or missing functions
- Interface errors
- Errors in data structures or external database access
- Behavior or performance errors
- Initialization and termination errors
Black Box Testing – Example
A tester, without knowledge of the internal structures of a website, tests the web pages by using a browser; providing inputs (clicks, keystrokes), and verifying the outputs against the expected outcome.
Levels applicable
This method is applicable to all levels of the software testing process:
- Unit Testing
- Integration Testing
- System Testing
- Acceptance Testing
The higher the level, and hence the bigger and more complex the box, the more black box testing method comes into use.
Black Box Testing techniques
Techniques that can be used for designing black box tests.
- Equivalence partitioning
Equivalence Partitioning is a software test design technique that involves dividing input values into valid and invalid partitions and selecting representative values from each partition as test data. - Boundary Value Analysis
Boundary Value Analysis is a software test design technique that involves the determination of boundaries for input values and selecting values that are at the boundaries and just inside/outside the boundaries as test data. - Cause Effect Graphing
Cause Effect Graphing is a software test design technique that involves identifying the cases (input conditions) and effects (output conditions), producing a Cause-Effect Graph, and generating test cases accordingly.
Black Box Testing – Advantages
- Tests are done from a user’s point of view and will help in exposing discrepancies in the specifications
- Tester need not know programming languages or how the software has been implemented
- Tests can be conducted by a body independent from the developers, allowing for an objective perspective and the avoidance of developer-bias
- Test cases can be designed as soon as the specifications are complete
Black Box Testing – Disadvantages
- Only a small number of possible inputs can be tested, and many program paths will be left untested
- Without clear specifications, which is the situation in many projects, test cases will be difficult to design
- Tests can be redundant if the software designer/ developer has already run a test case
- Ever wondered why a soothsayer closes his eyes when foretelling events? Almost so is the case in Black Box Testing
ISTQB definition
- 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.
