Domain Testing: Divide and Conquer - Testing Education

To assert that the output value Z assumes the correct value for all input values of
X and Y, we have to test all possible assignment values of X and Y. Assume that
X and Y take integer values.
If the program is being tested on a computer for which the word size is 32 bits
then the total possible values for X and Y, each are 2 32 .Since the combination of
X and Y yields Z, we have to test X and Y in combination.
The total possible combinations for X and Y are 2 32 x 2 32
Now, if we assume that the program takes about a millisecond to execute once,
we will need more than 50 billion years to completely test this program!
If testing a program as simple as this can lead to combinatorial explosion and
make testing seem impossible, imagine what happens with huge complicated
programs having hundreds of variables? This is where domain testing comes to
our rescue by helping us systematically reduce an infinitely large input domain to
few manageable sub-domains and then helping us choose the best test cases from
each sub-domain, thereby reducing out testing effort (time, money, labor, etc…)
drastically.
Step 7: Apply boundary value analysis, wherever applicable, to pick best test cases
from each sub-domain.
Rather than selecting any arbitrary element in an equivalence class as being the best
representative, the boundary-value analysis requires that one or more elements be
selected such that each edge (border) of the equivalence class is the subject of a test.
Hence, values on the boundary and values just off the boundary (below and/or beyond,
whatever is applicable) are selected in an equivalence class to be the best representatives
or test cases for that equivalence class.
What are the pitfalls of boundary-value analysis?
• Boundary-value analysis works well only when the program to be tested is
a function of several independent variables that represent bounded
physical quantities. In other words, boundary value analysis does not find
© Sowmya Padmanabhan, 2003
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