Equivalence partitioning:
Equivalence Partitioning determines the number of test cases for a given scenario.
Equivalence partitioning is a black box testing technique with the following goal:
1.To reduce the number of test cases to a necessary minimum.
2.To select the right test cases to cover all possible scenarios.

EP is applied to the inputs of a tested component. The equivalence partitions are usually derived from the specification of the component's behavior. An input has certain ranges which are valid and other ranges which are invalid. This may be best explained at the following example of a function which has the pass parameter "month" of a date. The valid range for the month is 1 to 12, standing for January to December. This valid range is called a partition. In this example there are two further partitions of invalid ranges. The first invalid partition would be <= 0 and the second invalid partition would be >= 13.

. ... -2 -1 0 1 .............. 12 13 14 15 .....
invalid partition 1 valid partition invalid partition 2

The testing theory related to equivalence partitioning says that only one test case of each partition is needed to evaluate the behavior of the program for the related partition. In other words it is sufficient to select one test case out of each partition to check the behavior of the program.

To use more or even all test cases of a partition will not find new faults in the program. The values within one partition are considered to be "equivalent". Thus the number of test cases can be reduced considerably.

Equivalence partitioning is no standalone method to determine test cases. It has to be supplemented by boundary value analysis. Having determined the partitions of possible inputs the method of boundary value analysis has to be applied to select the most effective test cases out of these partitions.


Boundary Value Analysis :

Boundary Value Analysis determines the effectiveness of test cases for a given scenario. To set up boundary value analysis test cases the tester first has to determine which boundaries are at the interface of a software component. This has to be done by applying the equivalence partitioning technique. Boundary value analysis and equivalence partitioning are inevitably linked together.

For the example of the month a date would have the following partitions: .
.. -2 -1 0 1 .............. 12 13 14 15 .....
--invalid partition 1 valid partition invalid partition 2

By applying boundary value analysis we can select a test case at each side of the boundary between two partitions . In the above example this would be 0 and 1 for the lower boundary as well as 12 and 13 for the upper boundary. Each of these pairs consists of a "clean" and a "dirty" test case. A "clean" test case should give a valid operation result of the program. A "dirty" test case should lead to a correct and specified input error treatment such as the limiting of values, the usage of a substitute value, or in case of a program with a user interface, it has to lead to warning and request to enter correct data.
The boundary value analysis can have 6 test cases: n, n-1, and n+1 for the upper limit; and n, n-1, and n+1 for the lower limit.
Note: As per the ISTQB standard the BVA will be " lower boundary -1between the boundary upper boundary +1", so boundary value analysis can have 4 test cases i.e. n & n+1 for the upper limit and n & n-1 for the lower limit.
Example:
An input field takes the year of birth between 1900 and 2004
The boundary values for testing this field are
A. 0,1900,2004,2005
B. 1900, 2004
C. 1899,1900,2004,2005
D. 1899, 1900, 1901,2003,2004,2005

Practically the Correct answer would be D, but as per ISTQB standards the answer would be C.

Happy Testing,

Javed Nehal