Black Box Testing Techniques

* Graph Based Testing Methods - Software testing begins by creating a graph of important objects and their relationships and then devising a series of tests that will cover the graph so that each objects and their relationships and then devising a series of tests that will cover the graph so that each object and relationship is exercised and error is uncovered.

* Error Guessing - Error guessing is a skill that is well worth cultivating since it can make testing much more effective and efficient - two extremely important goals in the testing process. Typically, the skill of Error Guessing comes with experience with the technology and the project. Error Guessing is the art of guessing where errors can be hidden. There are no specific tools and techniques for this, but you can write test cases depending on the situation: Either when reading the functional documents or when you are testing and find an error that you have not documented.

* Boundary Value Analysis - In boundary value analysis, test cases are generated using the extremes of the input domaini, e.g. maximum, minimum, just inside/outside boundaries, typical values, and error values. BVA is similar to Equivalence Partitioning but focuses on "corner cases".

Advantages of Boundary Value Analysis
1. Robustness Testing - Boundary Value Analysis plus values that go beyond the limits
2. Min - 1, Min, Min +1, Nom, Max -1, Max, Max +1
3. Forces attention to exception handling
4. For strongly typed languages robust testing results in run-time errors that abort normal execution

Limitations of Boundary Value Analysis
BVA works best when the program is a function of several independent variables that represent bounded physical quantities
1. Independent Variables
o NextDate test cases derived from BVA would be inadequate: focusing on the boundary would not leave emphasis on February or leap years
o Dependencies exist with NextDate's Day, Month and Year
o Test cases derived without consideration of the function
2. Physical Quantities
o An example of physical variables being tested, telephone numbers - what faults might be revealed by numbers of 000-0000, 000-0001, 555-5555, 999-9998, 999-9999?

* Equivalence Partitioning - Equivalence partitioning is a black box testing method that divides the input domain of a program into classes of data from which test cases can be derived.
EP can be defined according to the following guidelines:
1. If an input condition specifies a range, one valid and one two invalid classes are defined.
2. If an input condition requires a specific value, one valid and two invalid equivalence classes are defined.
3. If an input condition specifies a member of a set, one valid and one invalid equivalence class is defined.
4. If an input condition is Boolean, one valid and one invalid class is defined.

* Comparison Testing - There are situations where independent versions of software be developed for critical applications, even when only a single version will be used in the delivered computer based system. It is these independent versions which form the basis of a black box testing technique called Comparison testing or back-to-back testing.

* Orthogonal Array Testing - The Orthogonal Array Testing Strategy (OATS) is a systematic, statistical way of testing pair-wise interactions by deriving a suitable small set of test cases (from a large number of possibilities).