Domain Testing: Divide and Conquer - Testing Education

There have been several discussions in the literature about the relative
merits of partition testing and pure random testing. Pure random testing is not
random selection of test cases from subdomains, but is just random selection of test
cases from the entire input domain without forming any partitions. Random and
partition testing have been found to be better than each other under certain
conditions, and the two are almost equivalent under certain other conditions.
Proportional partition testing has mostly been discussed as a method that
evolved in order to improve partition testing and to make its effectiveness at
finding failures greater than that of random testing. Weyuker and Jeng (1991) noted
that when the original partition testing method is refined so that we form all
subdomains of equal size and then select an equal number of test cases from each
subdomain, pure random testing can never beat partition testing in terms of
effectively finding failures. This is assuming that either the number of subdomains
formed is very large or the number of test cases chosen from each subdomain is
very large compared to the size of the subdomain itself.
Chan et al. (1998) cited a modified version of the proportional partition
testing method that somewhat blends the refined version of partition testing
described by Weyuker and Jeng (1991) with the traditional proportional partition
testing method.
Chan et al. (1998) called their method the Optimally Refined Proportional
Sampling (ORPS) strategy. This method involves partitioning the input domain into
equally sized partitions as described by Weyuker and Jeng (1991), and then
selecting one test case at random from each equally sized subdomain.
Chan et al. (1998) noted that the results of trying out their ORPS strategy on
several programs seemed positive enough to recommend this method as a
subdomain testing strategy.
Ntafos (1998) has illustrated an experiment in which he compared random
testing with proportional partition testing. When doing proportional partition
testing, he considered 50 subdomains. He applied the two strategies to 50 test cases
to start with, and then increased to 2,000 total test cases in increments of 50 cases.
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