appendix 1. analyzing the triangle problem - Testing Education

ANALYZING THE TRIANGLE PROBLEM
(Continued)
1. Verify that invalid inputs are rejected as expected (continued).
(b) j is not valid
The same types of tests are needed as for j as were needed for i.
(c) k is not valid
The same types of tests are needed as for k as were needed for i.
How much testing of the second and third input lengths, j and k, is appropriate?
If we can assume that the software engineer who developed the triangle software is
reasonably competent, we can also assume with confidence that the software engineer
would have provided one common subroutine to edit all of i, j and k at the time they are
input.
In this situation, a comprehensive set of test cases for j and k, following the
comprehensive set of tests for i, is unnecessary. The first set of test cases for i will
already have extensively exercised the common edit routine, so re-testing for several
values of j and k would be redundant. If the software works for i, it should also work for j
and for k.
Only one additional test case is needed for j, and also one for k, to double-check that the
software engineer at least remembered to call or access the common edit routine for j
and k as well as for i.
A better approach (instead of many negative test cases for i, followed by only one each
for j and k), is to spread the set of negative test cases equally among i, j and k.
However, if we are paranoid, we will be willing to assume nothing. Since this is a black
box test, we do not know for sure how the software was constructed internally. Although
it may be an incompetent practice, the software engineer may have written three separate
input edit routines, one each for i, j and k. In this circumstance, the fact that the first set
of tests for i work correctly will predict nothing about the behavior of j and k.
Copyright 2004 Collard 13 & Company
Appendix 1
13