8.1 I Review 217
8.11
If you want to choose as a hypothesis that the problem is one that the
programmer makes frequently, you need records on the root causes of previ-
ous defects diagnosed in the system in question. If you want to choose as a
hypothesis that the problem is one of the most common errors made when
using the particular programming language selected for this application,
consult an error checklist from a programming text, or Appendix A.
If you want to choose as a hypothesis that the problem is one of the
most common errors made by all programmers, you might find it useful to
consult Chapter 11. If you want to choose as a hypothesis that the problem
is in recently changed code, you need to have been using a source control
system.
Review
Debugging heuristics don't lend themselves to easy categorization, as strate-
gies and tactics do.
The first heuristic to apply is often called
stabilizing the problem.
The
goal of stabilization is reproducibility. The first step in stabilizing a program
is to obtain an undesired behavior each time the program executes. The
next step is to obtain the same undesired behavior each time the program
executes. The third step is to obtain the same undesired behavior in differ-
ent environments. The fourth step is to obtain the same undesired behavior
on different platforms.
The second heuristic to apply is to create a standalone test case. A test
case typically has two parts: the program and the input data. We present
heuristics for creating test case programs and test input data.
To cut down a file-oriented application into a standalone test, create a
file that contains the inputs required to get the program just prior to the
point where the problem occurs. Insert a call to record the program state
just prior to the problem. Run the program with the log file, capture the
program state, build a new driver that sets that state directly, and replace the
old driver with the new one.
To cut down a GUI application into a standalone test, create a log that
contains the mouse and keyboard actions required to get the program just
prior to the point where the problem occurs. Insert a call to record the pro-
gram state just prior to the problem. Run the program with the log file,
capture the program state, build a new driver that sets that state directly,
and replace the old driver with the new one.
I Chapter 8

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