Black-Box Testing (Functional)

Software testing, as a separate process, witnessed vertical growth and received the attention of project stakeholders and business sponsors in the last decade. Various new techniques have been continuously introduced. Apart from the traditional testing techniques, various new techniques necessitated by the complicated business and development logic were realized to make software testing more meaningful and purposeful. This part discusses some of the popular testing techniques that have been adopted by the testing community.

Black-Box Testing (Functional)

In black-box, or functional testing, test conditions are developed on the basis of the program or system's functionality; that is, the tester requires information about the input data and observed output, but does not know how the program or system works. Just as one does not have to know how a car works internally to drive it, it is not necessary to know the internal structure of a program to execute it. The tester focuses on testing the program's functionality against the specification. With black-box testing, the tester views the program as a black box and is completely unconcerned with the internal structure of the program or system. Some examples in this category include decision tables, equivalence partitioning, range testing, boundary value testing, database integrity testing, cause—effect graphing, orthogonal array testing, array and table testing, exception testing, limit testing, and random testing.

A major advantage of black-box testing is that the tests are geared to what the program or system is supposed to do, which is natural and understood by everyone. This should be verified with techniques such as structured walkthroughs, inspections, and joint application designs (JADs). A limitation is that exhaustive input testing is not achievable, because this requires that every possible input condition or combination be tested. In addition, because there is no knowledge of the internal structure or logic, there could be errors or deliberate mischief on the part of a programmer that may not be detectable with black-box testing. For example, suppose a payroll programmer wants to insert some job security into a payroll application he is developing. By inserting the following extra code into the application, if the employee were to be terminated, that is, his employee ID no longer existed in the system, justice would sooner or later prevail:

if my employee ID exists
deposit regular pay check into my bank account
else
deposit an enormous amount of money into my bank account
erase any possible financial audit trails
erase this code