Introduction to Black Box Testing Techniques

Firstly let us understand the meaning of Black Box Testing.

The term 'Black Box' refers to the software, which is treated as a black box. By treating it as a black box, we mean that the system or source code is not checked at all. It is done from customer's viewpoint. The test engineer engaged in black box testing only knows the set of inputs and expected outputs and is unaware of how those inputs are transformed into outputs by the software.

Types of Black Box Testing Techniques: Following techniques are used for performing black box testing

1) Boundary Value Analysis (BVA)

2) Equivalence Class Testing

3) Decision Table based testing

4) Cause-Effect Graphing Technique

1) Boundary Value Analysis (BVA):

This testing technique believes and extends the concept that the density of defect is more towards the boundaries. This is done to the following reasons

a) Usually the programmers are not able to decide whether they have to use <= operator or < operator when trying to make comparisons.

b) Different terminating conditions of For-loops, While loops and Repeat loops may cause defects to move around the boundary conditions.

c) The requirements themselves may not be clearly understood, especially around the boundaries, thus causing even the correctly coded program to not perform the correct way.

Strongly typed languages such as Ada and Pascal permit explicit definition of variable ranges. Other languages such as COBOL, FORTRAN and C are not strongly typed, so boundary value testing is more appropriate for programs coded in such languages.


2) Equivalence Class Testing:

The use of equivalence classes as the basis for functional testing is appropriate in situations like

a) When exhaustive testing is desired.

b) When there is a strong need to avoid redundancy.

The above are not handled by BVA technique as we can see massive redundancy in the tables of test cases. In this technique, the input and the output domain is divided into a finite number of equivalence classes.

3) Decision Table Based Testing:

Decision tables are a precise and compact way to model complicated logic. Out of all the functional testing methods, the ones based on decision tables are the most rigorous due to the reason that the decision tables enforce logical rigour.

Decision tables are ideal for describing situations in which a number of combinations of actions are taken under varying sets of conditions.

 
4) Cause-Effect Graphing Technique:

This is basically a hardware testing technique adapted to software testing. It considers only the desired external behaviour of a system. This is a testing technique that aids in selecting test cases that logically relate Causes (inputs) to Effects (outputs) to produce test cases.

A “Cause” represents a distinct input condition that brings about an internal change in the system. An “Effect” represents an output condition, a system transformation or a state resulting from a combination of causes.