Some Black box testing techniques...Graph based testing methods, Error guessing and Boundary Value Analysis.

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 relationship is exercised and errors are uncovered.Graph based testing begins with the definition of all nodes and node weights i.e. objects and attributes are identified.

Error Guessing
The purpose of error guessing is to focus the testing activity on areas that have not been handled by the other more formal techniques, such as equivalence partitioning and boundary value analysis. It comes with an experience of technology and the project. There are no specific tools and techniques for error guessing but you can write test cases depending on the situation. Error guessing will require tester to think out of the box and would involve intuition and experience of the tester.

Boundary Value Analysis (BVA)
It is a test data selection technique where the extreme values are chosen. It makes use of the fact that the inputs and outputs of the component under test can be partitioned into ordered sets with identifiable boundaries. A test engineer chooses values that lie along data extremes. It is expected that if the system works correctly for these special values, then it will work correctly for all values in between. The boundary value analysis test cases are obtained by holding the values of all but one obtained by holding the values of all but one variable at their nominal values, and letting that variable at their nominal values, and letting that variable assume its extreme values variable assume its extreme value.
There are two ways to generalize BVA technique :
- By the number of variables: for n variables, BVA yields 4n+1 test cases.
- By the kinds of ranges.

Advantages of Boundary Value Analysis
- Robustness Testing
- It checks values for min-1, min, nom, max-1, max, max+1
- It forces attention to exception handling.

Limitations of Boundary Value Analysis
BVA works best when the program is a function of several independent variables that represent bounded physical quantities.
Boundary value analysis works well when the program to be tested is a function of the program to be tested is a function of several severalindependent independent variables that variables that represent bounded represent bounded physical physicalquantities quantities.