Black box testing and its advantages and disadvantages

What is 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.

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.

 

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 of 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.

Black Box Testing Techniques :

Following are some techniques that can be used for designing black box tests.

• Equivalence partitioning
• Boundary Value Analysis
• Cause Effect Graphing

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.

Click to know about White box testing and Gray box testing and Differences between Black Box and White Box Testing and Compare Quality-Assurance, Quality-Control, Testing