Difference between Equalance class partion and boundary
value analysis?

Answer Posted / kanad

The main difference between EP and BVA is that EP
determines the number of test cases to be generated for a
given scenario where as BVA will determine the effectivenss
of those generated test cases.

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.
EV is applied to the inputs of a tested component. The
equivalence partitions are usually derived from the
specification of the component's behaviour.

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 behaviour 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 behaviour 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 stand alone 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.

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