Overview of Testing - Software Testing: Testing Across the Entire Software Development Life Cycle - page 14

product deadline. Ironically, just the opposite is true. The longer the delay in
discovering defects in the software under development, the more expensive it is to
correct the defect just prior to software release.
After spending a professional career measuring and analyzing the industry-wide
practices of software development, Drs. Basili and Boehm computed some industry
average costs of correcting defects in software under development. Figure 1.2 is an
irrefutable proof of the axiom “test early and test often.” [10A] The numbers fi rst
published in 1996 were revalidated in 2001.

Figure 1.2

Defect correction cost profile for the software industry

At the beginning of a software development project, there is no code, just design
documentation. If the design documentation is properly tested (called static testing,
see Chapter 6), then the cost of correction is the cost of revising the documentation.
This is typically done by a technical writer at relatively small personnel cost after the
application-knowledgeable development management provides the correction. Basili
fi nds the average cost to revise a document defect is $25.
As software code (considered fair game for static testing) is written and code
execution begins, the cost of a correction rises to $139, primarily due to the expense
of programmer effort. Several kinds of testing can be done; however, the code defect
resolution at this development phase is correcting the code.
As pieces of program code are completed and tested, they are knitted together,
or integrated into la rger program modules that begin to perfor m meaningful business
tasks. The cost of correcting these larger units of code more than doubles to $455
due to the additional time it takes to diagnose the problem in more complex code and
the additional time needed to disassemble the code module into correctable pieces,
correct the code, and then reassemble the code module for retesting.
As the software development team draws closer to the application or product
completion, more program modules are brought together into the fi nal delivery
package. Capers estimates the cost of defect correction at this stage doubles to $7,136