Black Box Testing

DEFINITION

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.

Black Box Testing is contrasted with White Box Testing. 

Black Box Testing 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

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 TO

Black Box Testing 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.

TEST DESIGN TECHNIQUES

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 determination of boundaries for input values and selecting values that are at the boundaries and just inside/outside of 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.

ADVANTAGES OF BLACK BOX TESTING

• 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

DISADVANTAGES OF BLACK BOX TESTING

• 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 the eyes when foretelling events? So is almost the case in Black Box 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.